Updated October 2026 | Long COVID, brain fog, cognitive fatigue and post-exertional malaise
AI Answer: Why Does Thinking Make Long COVID Worse?
Thinking can make Long COVID symptoms worse because mental activity is a form of exertion. Reading, concentrating, making decisions, speaking and processing information can trigger cognitive fatigue, headaches, dizziness, brain fog and, in some people, post-exertional malaise (PEM).
Researchers are investigating several possible biological contributors, including autonomic dysfunction, changes in brain blood flow, inflammation and blood–brain barrier abnormalities. However, no single mechanism has been established to explain why cognitive effort triggers symptoms in every person with Long COVID.
For people who experience cognitive PEM, pacing mental activity may help reduce repeated symptom exacerbations.
Key Takeaways
- Mental effort is still exertion. A person does not need to exercise physically to experience symptom worsening.
- Brain fog and PEM are different. Brain fog describes cognitive difficulties; PEM involves a worsening of symptoms following exertion and may be delayed.
- Talking can be particularly demanding. Conversation combines listening, language processing, memory, attention and social interaction.
- Symptoms may appear later. Someone may manage an activity while it is happening but experience deterioration afterwards.
- Research has identified measurable neurological abnormalities in some people with Long COVID, although these findings do not yet explain every cognitive symptom.
- Pacing is about managing current capacity, not pushing through symptoms or following a fixed programme of increasing cognitive effort.
When Thinking Becomes Exhausting
For many people living with Long COVID, the most exhausting part of the day isn’t walking, standing or lifting something heavy.
It’s thinking.
It’s trying to follow a conversation, remember what someone said, answer an email or concentrate long enough to read a few pages.
A phone call that once felt routine can leave you needing to lie down. A video meeting may trigger a headache. An appointment that involves listening, remembering information and answering questions can consume the energy you had available for the rest of the day.
Sometimes the consequences don’t arrive until later.
You finish the conversation feeling reasonably pleased that you managed it. Then, several hours afterwards, the brain fog becomes worse, your body feels heavier and even simple decisions become difficult.
At first, it seems rather absurd.
You’ve been sitting in a chair. You haven’t run anywhere. You may barely have moved.
So why does your body behave as though you’ve done something physically demanding?
The answer begins with something we rarely think about when we’re healthy: mental activity requires physiological work, even when the body appears to be resting.
But the relationship between cognitive effort and Long COVID is more complicated than simply saying the brain has run out of energy.
What Is Cognitive Exertion?
Cognitive exertion is the mental effort involved in processing information, concentrating, remembering, planning, making decisions and communicating.
It includes activities that may not look demanding from the outside.
Reading a document, following instructions, completing a form, listening to several people talking or making a series of decisions can all require sustained attention.
Even an enjoyable conversation can be cognitively demanding.
In everyday life, these processes usually happen without much conscious effort. We move between tasks, filter distractions and retrieve information without thinking about the work involved.
With Long COVID, some people experience difficulties with attention, memory, processing speed and executive function — the mental processes involved in planning, organising and managing tasks.
These difficulties are often described collectively as brain fog.
However, brain fog is a description of symptoms, not a single diagnosis or a complete explanation of their cause.
Cognitive exertion can make existing brain fog worse, but it can also trigger other symptoms, including physical exhaustion, headaches, dizziness or a broader post-exertional deterioration.
Brain Fog, Cognitive Fatigue and PEM: What’s the Difference?
These terms are often used interchangeably, but they describe different experiences.
Brain fog refers to cognitive difficulties such as poor concentration, forgetfulness, slower processing or difficulty finding words.
Cognitive fatigue describes mental exhaustion or reduced ability to sustain cognitive activity. Someone may become increasingly unable to concentrate after reading, working or talking.
Post-exertional malaise (PEM) is a worsening of symptoms after exertion. It may involve cognitive symptoms, but it can also affect sleep, pain, autonomic symptoms and general physical functioning.
PEM can be delayed, sometimes appearing hours or a day or more after the triggering activity, and recovery may take days or longer.
A person can experience brain fog without every episode being PEM.
Equally, someone with PEM may experience a broader symptom relapse after mental activity rather than simply feeling tired.
This distinction matters because the appropriate response depends partly on what is happening.
For someone with PEM, repeatedly pushing through cognitive symptoms may lead to further symptom exacerbation.
For a fuller explanation, read our guide to post-exertional malaise in Long COVID.
What Does Research Tell Us About Cognitive Problems in Long COVID?
Cognitive symptoms are among the most frequently reported and disabling aspects of Long COVID.
Research has increasingly moved beyond asking whether people experience brain fog to examining measurable differences in cognitive performance and possible biological mechanisms.
Several findings are particularly interesting.
1. Large Studies Have Identified Measurable Cognitive Differences
A major study published in The New England Journal of Medicine in 2024 examined cognitive performance among participants with different experiences of SARS-CoV-2 infection.
Researchers identified measurable differences in cognitive performance, particularly involving memory, reasoning and executive function.
Participants with persistent unresolved symptoms generally showed greater average deficits than those whose symptoms had resolved.
The findings are important because they demonstrate that post-COVID cognitive difficulties can be measurable using standardised research assessments.
However, average differences between groups do not determine an individual’s cognitive ability, and they should not be used to predict how severely a particular person will be affected.
The research also did not establish that every episode of cognitive fatigue or PEM is caused by the same neurological process.
2. Researchers Have Found Blood–Brain Barrier Abnormalities
In February 2024, researchers led by Chris Greene published a study in Nature Neuroscience examining blood–brain barrier function in people with Long COVID-associated cognitive impairment.
The blood–brain barrier helps regulate movement of substances between the bloodstream and the brain.
Using specialised MRI techniques, researchers found increased blood–brain barrier permeability in a small group of people with Long COVID and brain fog compared with participants without cognitive symptoms.
The imaging component included 32 people across recovered and Long COVID groups.
The researchers also identified inflammatory and vascular-related changes that may be relevant to neurological symptoms.
These findings provide objective evidence of a possible biological contributor to cognitive impairment in a subset of patients.
But the study was relatively small.
It does not establish that everyone with Long COVID brain fog has blood–brain barrier disruption, or that this mechanism explains why talking, reading or concentrating triggers delayed PEM.
Larger studies and further research are needed.
3. Subjective Brain Fog and Cognitive Testing Do Not Always Match
A 2024 study published in Scientific Reports examined 162 participants, including 50 people with post-COVID syndrome.
Researchers compared self-reported cognitive problems with performance on computerised cognitive tasks.
Interestingly, subjective complaints and objective test results did not always correspond closely.
This does not mean that reported cognitive difficulties are imaginary.
It means that different methods measure different aspects of cognitive functioning.
A person may perform adequately during a brief test but struggle with sustained concentration, multitasking or repeated cognitive demands throughout an ordinary day.
The study also identified associations involving fatigue, perceived stress and cognitive performance. These findings should not be interpreted as evidence that Long COVID cognitive symptoms are simply caused by anxiety.
One of the remaining research challenges is developing assessments that capture real-world cognitive limitations more accurately.
4. Cognitive Treatments Are Being Tested, but Evidence Remains Limited
A randomised clinical trial from the RECOVER-NEURO programme, published in JAMA Neurology in 2026, evaluated several interventions for cognitive symptoms in Long COVID.
The trial included 328 participants and investigated approaches involving computerised cognitive training, structured cognitive rehabilitation and transcranial direct current stimulation.
The primary results did not establish a clear superiority of the tested active interventions over their relevant comparators.
Participants across groups reported some improvement, but improvement within a group is not proof that the intervention itself caused the change.
This is particularly important when interpreting claims about brain-training programmes or neurological stimulation.
The trial contributes useful evidence, but it does not establish a proven treatment for cognitive PEM.
And for people whose cognitive activity triggers significant post-exertional worsening, the demands of any proposed rehabilitation programme need careful consideration.
Why Can Thinking Trigger Physical Symptoms?
The brain is constantly active, even at rest.
Cognitive tasks involve networks responsible for attention, memory, language, sensory processing and decision-making.
These processes depend on coordinated neurological and physiological systems.
Researchers are investigating several ways Long COVID may interfere with those systems.
Autonomic Nervous System Dysfunction
The autonomic nervous system helps regulate heart rate, blood pressure, circulation and other functions that normally operate without conscious effort.
Some people with Long COVID develop autonomic dysfunction, including postural orthostatic tachycardia syndrome (POTS).
Symptoms can include dizziness, palpitations, fatigue, difficulty concentrating and intolerance of upright posture.
For someone with orthostatic intolerance, a cognitive task performed while sitting upright may involve both mental and postural demands.
That can make it difficult to separate the effects of thinking from the effects of remaining upright.
You can explore this further in our article on POTS and dysautonomia in Long COVID.
Changes in Brain Blood Flow and Vascular Regulation
Researchers have also investigated changes in cerebral blood flow and vascular regulation in people with Long COVID and related post-infectious conditions.
Some studies suggest that altered circulation may contribute to symptoms in particular patient groups.
However, it remains uncertain how directly these findings explain cognitive exertion intolerance, and not every person with Long COVID will have the same abnormalities.
Inflammation and Neuroimmune Changes
Persistent immune activation and inflammatory signalling are being studied as possible contributors to cognitive symptoms.
The 2024 blood–brain barrier research adds to this area of investigation.
But identifying inflammatory abnormalities does not automatically establish a direct causal pathway between a particular cognitive task and a later symptom crash.
Cellular Energy Metabolism
Researchers are also investigating changes in cellular energy metabolism and responses to exertion in Long COVID.
This is a promising area of research, but it is important not to turn an emerging hypothesis into a settled explanation.
At present, there is no single established biological mechanism that explains cognitive exertion intolerance in every person with Long COVID.
Why Is Talking So Exhausting?
Talking is one of those activities we rarely consider demanding until it becomes difficult.
A conversation involves far more than producing words.
You are listening, interpreting language, remembering what has already been said, deciding how to respond and monitoring the other person’s reactions.
You may also be filtering background noise, maintaining eye contact and trying to organise your thoughts quickly enough to keep the conversation moving.
And unlike reading, conversation often provides very little opportunity to pause.
The other person is waiting for an answer.
Sometimes they ask another question before you’ve finished processing the first.
For someone with cognitive dysfunction, that combination of demands may be particularly difficult.
It may help explain why some people find written messages easier than phone calls, or one-to-one conversations easier than group discussions.
These are individual experiences rather than universal rules.
Some people find reading more exhausting than speaking. Others struggle most with listening or processing speech.
The important point is that conversation can be a significant cognitive activity even when it looks effortless to everyone else.
Why Can Video Calls Be Worse?
Video calls combine several demands: sustained attention, auditory processing, visual information, social interaction and often screen exposure.
Depending on the person, they may also involve sensitivity to light, sound, movement or competing information.
A video meeting may therefore be more difficult than a short telephone call.
But it is not necessarily more exhausting for everyone.
Some people prefer video calls because seeing facial expressions helps them follow speech. Others find in-person interaction harder because of travel, posture or sensory stimulation.
The most useful approach is to identify which format is least demanding for the individual.
If noise and light are major triggers, our article on sensory overload in Long COVID explores why everyday environments can become overwhelming.
Why Do Symptoms Sometimes Appear Hours Later?
One of the most confusing aspects of PEM is the delay.
You may finish an appointment feeling tired but reasonably functional.
Later that evening, or the following day, symptoms may become substantially worse.
This makes it difficult to identify triggers.
A person may blame a short walk in the afternoon without realising that a demanding morning meeting also contributed to their total exertion.
Physical, cognitive, emotional and sensory demands can overlap.
Researchers have not established one complete explanation for the delayed timing of PEM.
Inflammatory, autonomic and metabolic processes are being investigated, but their relative roles remain uncertain.
What matters practically is recognising that the absence of immediate symptoms does not always mean an activity was well tolerated.
The Invisible Cost of Looking Well
One of the hardest things about cognitive exertion is that it is almost completely invisible.
Someone watching you answer emails or have a conversation may assume you are coping well.
They see you speaking clearly, responding appropriately and perhaps even making a joke.
They do not necessarily see what happens afterwards.
The headache, the dizziness, the loss of concentration or the need to spend the following day resting.
This can create misunderstandings with friends, family, employers and sometimes healthcare professionals.
If you can hold a conversation during an appointment, people may assume you can manage similar conversations throughout the day.
But completing an activity once is not the same as being able to repeat it reliably.
That distinction also matters at work.
An employee may be able to attend a meeting yet struggle to sustain the same level of concentration over several hours.
For a broader discussion, see Long COVID and Work in the UK: Why People Are Leaving the Workforce.
How to Pace Cognitive Activity Without Making Life Even Smaller
Pacing is often discussed in relation to physical activity, but cognitive demands can also need managing.
The aim is not to avoid all thinking.
It is to understand your current limits, reduce unnecessary demands and avoid repeated symptom exacerbation where possible.
There is no single schedule that works for everyone, and pacing has not been established as a cure for Long COVID.
However, several practical strategies may help people manage cognitive demands.
Break Up Demanding Tasks
Instead of completing a long form or reading a lengthy document in one sitting, it may be easier to divide the activity into smaller sections.
For some people, even a few minutes of concentrated work can be demanding.
The appropriate duration depends on individual capacity, not an arbitrary target.
Reduce Multitasking
Trying to listen, write, remember instructions and respond simultaneously can increase cognitive demand.
Where possible, focus on one activity at a time.
Written instructions or short summaries may reduce the need to remember everything.
Choose the Least Demanding Communication Format
Some people find texting easier than speaking.
Others prefer voice messages because typing or reading is exhausting.
There is no universally best option.
The aim is to use the format that places the least demand on the person involved.
Allow Recovery Time
Consider whether demanding appointments, conversations or administrative tasks need to be separated.
For someone with PEM, scheduling several cognitively demanding activities on the same day may exceed their current capacity.
Recovery time should be based on symptoms rather than a fixed expectation of how quickly someone ought to improve.
Reduce Sensory Demands
A quiet room, lower screen brightness, fewer notifications or reduced background noise may make some tasks easier.
However, sensory preferences differ, and people should avoid assuming that one environmental adjustment will help everyone.
Avoid Pushing Through a Crash
If an activity repeatedly causes significant symptom worsening, continuing to increase its duration simply to build tolerance may be inappropriate.
People with PEM may need an individualised approach that respects their current energy limits.
For additional strategies, read our guide to pacing and managing PEM.
When Should Cognitive Symptoms Be Medically Assessed?
Persistent cognitive symptoms deserve appropriate clinical attention, particularly when they interfere with daily life, communication or work.
A clinician may consider other contributing or treatable problems, such as sleep disorders, medication effects, nutritional deficiencies, mood disorders or other neurological conditions.
These possibilities do not mean that Long COVID is psychological or that the person’s symptoms are not genuine.
They reflect the importance of not attributing every new symptom automatically to Long COVID.
Sudden confusion, new difficulty speaking, facial weakness, one-sided weakness or other abrupt neurological symptoms require urgent medical assessment. In the UK, call 999 if stroke is suspected.
Frequently Asked Questions
Why does thinking make Long COVID symptoms worse?
Mental activity is a form of exertion. Some people with Long COVID experience worsening cognitive or physical symptoms after concentration, reading, decision-making or conversation. Researchers are investigating possible neurological, autonomic, inflammatory and vascular contributors, but the mechanisms are not fully understood.
Can thinking trigger post-exertional malaise?
Yes. Cognitive exertion can trigger PEM in some people with Long COVID. The resulting symptom worsening may be delayed and can involve more than fatigue or brain fog.
Why is talking so exhausting with Long COVID?
Conversation requires listening, language processing, memory, attention and social interaction. Some people with Long COVID find these combined demands difficult to sustain, particularly when they also experience cognitive impairment or sensory sensitivity.
Why can I manage a conversation but feel worse afterwards?
Some people experience delayed symptom exacerbation after cognitive activity. This may be consistent with PEM, particularly when symptoms worsen beyond ordinary tiredness and recovery takes an unusually long time.
Is cognitive fatigue the same as brain fog?
Not exactly. Brain fog describes difficulties with cognitive functions such as concentration, memory and processing speed. Cognitive fatigue describes mental exhaustion or reduced capacity to sustain cognitive activity. They can occur together.
Can you have Long COVID brain fog with normal scans?
Yes. Routine brain imaging does not necessarily identify the causes of cognitive symptoms. Some research has identified abnormalities using specialised methods, but those findings are not established diagnostic tests for every patient with Long COVID.
Can brain-training exercises cure Long COVID brain fog?
No brain-training programme has been established as a cure. A 2026 randomised clinical trial did not demonstrate clear superiority of the tested active interventions over relevant comparators. People who experience PEM should be cautious about programmes that substantially increase cognitive exertion.
How can I reduce cognitive crashes?
Identifying triggers, reducing multitasking, adapting communication, allowing recovery time and pacing demanding activities may help some people. The approach should be individualised, particularly when PEM is present.
Can cognitive symptoms improve over time?
Some people experience improvement, while others have persistent or fluctuating difficulties. Recovery varies, and current research cannot reliably predict an individual’s outcome.
Living With Long COVID: Related Articles
- Post-Exertional Malaise (PEM): Understanding Symptom Crashes — Why physical and mental exertion can trigger delayed worsening.
- Sensory Overload in Long COVID — Understanding why noise, light and everyday stimulation can become exhausting.
- POTS and Dysautonomia in Long COVID — How autonomic symptoms can affect concentration, posture and daily functioning.
- Long COVID and Work in the UK — Why fluctuating symptoms and cognitive limitations can make employment difficult.
- Long COVID Loss of Identity — The emotional consequences of losing abilities that once felt ordinary.
- Redefining Strength: Coping with Long COVID — A personal reflection on adaptation and living with changing limitations.
Research and References
1. Hampshire A and colleagues (2024). Cognition and Memory after Covid-19 in a Large Community Sample.
New England Journal of Medicine.
A large study examining cognitive performance following SARS-CoV-2 infection, including differences associated with persistent symptoms.
2. Greene C and colleagues (2024). Blood–Brain Barrier Disruption and Sustained Systemic Inflammation in Individuals with Long COVID-Associated Cognitive Impairment.
Nature Neuroscience.
Investigated blood–brain barrier abnormalities and inflammatory changes in people with Long COVID-associated cognitive impairment.
3. Bland AR and colleagues (2024). Profiles of Objective and Subjective Cognitive Function in Post-COVID Syndrome, COVID-19 Recovered, and COVID-19 Naïve Individuals.
Scientific Reports.
Compared self-reported cognitive difficulties and objective cognitive performance across 162 participants.
4. Knopman DS and colleagues (2026). Evaluation of Interventions for Cognitive Symptoms in Long COVID: A Randomized Clinical Trial.
JAMA Neurology.
RECOVER-NEURO trial evaluating cognitive rehabilitation, computerised training and non-invasive brain stimulation approaches.
5. Davis HE, McCorkell L, Vogel JM, Topol EJ (2023). Long COVID: Major Findings, Mechanisms and Recommendations.
Nature Reviews Microbiology.
Comprehensive review of Long COVID mechanisms, clinical features and research priorities.
6. NICE. COVID-19 Rapid Guideline: Managing the Long-Term Effects of COVID-19 (NG188).
UK clinical guidance covering assessment and management of ongoing symptoms.
7. Centers for Disease Control and Prevention. Long COVID Clinical Guidance.
Information on Long COVID symptoms, PEM and clinical management.
Medical Disclaimer
This article is intended for educational and informational purposes and draws on published scientific research, clinical guidance and experiences commonly reported by people living with Long COVID.
It does not provide individual medical advice, diagnosis or treatment recommendations.
Research into the mechanisms of cognitive impairment and post-exertional malaise is ongoing. Findings from individual studies should not be interpreted as establishing one explanation or treatment for everyone with Long COVID.
Pacing and other symptom-management approaches should be adapted to individual circumstances and are not cures.
Seek advice from an appropriately qualified healthcare professional about persistent, worsening or unexplained symptoms. Sudden neurological symptoms require urgent assessment.
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