Brain fog

Brain fog is not a single disease. It describes a group of cognitive symptoms that make thinking feel slow, effortful, or unreliable. People describe brain fog in many ways:

• Trouble concentrating or holding your attention
• Forgetting words, names, or what you were about to do
• Losing your train of thought mid-sentence
• Difficulty following conversations, reading, planning, or making decisions
• Feeling mentally drained after short tasks, like a phone call or a meeting
• A sense that your thinking is "slower" than it used to be
• Being overwhelmed by noise, light, or too much going on

For many people, the most difficult part is not a single symptom, but how quickly the brain tires. A task that used to be easy now takes all your energy, and afterwards you need to rest.

Common and treatable

• Poor or unrefreshing sleep, including sleep apnoea
• Low iron, anaemia, or vitamin B12 deficiency
• Thyroid problems
• Blood sugar problems
• Medicines, for example some older antihistamines, sleeping pills, strong painkillers, and some medicines for mood or epilepsy
• Alcohol
• Stress, depression, or anxiety, which can both cause brain fog and exist alongside other causes
• Hormonal changes, for example around menopause

Linked to long COVID and post infectious conditions

• Long COVID. Brain fog is one of its most common symptoms.
• POTS and other dysautonomia. Less blood reaches the brain when you are upright, so thinking is often worse when standing and better lying down. Read the POTS guide.
• Post exertional malaise (PEM). Brain fog often gets much worse a day or two after physical or mental effort.
• ME/CFS. Problems with thinking and memory are a core feature.
• MCAS. Some people notice brain fog during flares. Read the MCAS guide.

Less common, but important

New memory problems that keep getting worse, especially in older adults, or confusion that comes on suddenly, need a proper medical assessment to rule out other conditions.

Researchers are still working this out. Studies point to several possible mechanisms: ongoing inflammation, changes in blood flow to the brain, problems with the autonomic nervous system, and disrupted sleep. Large studies have shown that some people have measurable changes in memory and thinking after COVID, so this is not imagined.

For many people, brain fog after COVID slowly improves. For others it lasts for a long time. Either way, there are often things that can be treated or made easier.

• Worse when standing, better when lying down. Could be POTS or another form of dysautonomia.
• Worse a day or two after doing too much. Could be PEM.
• Worse after meals, heat, or with flushing or itching. Could be linked to POTS or MCAS.
• Worse after a bad night. Sleep may be part of the problem.
• Started with a new medicine. Talk to the doctor who prescribed it.
• Comes with low mood or loss of interest. Depression can cause or add to brain fog.

Writing down when your brain fog is better and worse, even for a week or two, can help a lot.

There is no single test for brain fog. The aim is to find causes that can be treated. What your healthcare provider can check:

• Blood tests, for example blood count, iron levels (ferritin), vitamin B12, folate, thyroid function, and blood sugar
• A review of your medicines
• Questions about sleep, mood, and stress
• Heart rate and blood pressure lying and standing, if your symptoms are worse when upright

There is no single cure, but a combination of practical strategies helps most people function better while they recover.

• Pace your mental energy. Treat thinking as a limited daily budget. Break tasks into short pieces, rest before you are exhausted, and stop before a crash rather than pushing through.
• Do one thing at a time. Multitasking drains a tired brain fast.
• Use tools instead of memory. Lean on lists, calendars, alarms, reminders, and notes. Do demanding tasks at your best time of day, and reduce noise, screens, and distractions.
• Protect your sleep. Keep regular times, and raise sleep problems with your doctor, since unrefreshing sleep strongly worsens fog.
• Treat what is treatable. If you also have a fast heart rate on standing, dizziness, low iron, thyroid problems, low mood, or sleep apnoea, treating these often improves thinking. Increasing fluid and salt can help if a blood flow problem is contributing.
• Return to activity gradually. Structured cognitive rehabilitation and a slow, graded return to demanding tasks help some people, ideally guided by a clinician who understands post viral illness.

Medicines are sometimes tried for persistent brain fog, but the evidence is still limited and any medicine should be decided with a doctor.

Call or go to the emergency department if you have:

• Sudden confusion
• Sudden weakness or numbness, especially on one side
• Sudden trouble speaking or understanding, or facial drooping
• A sudden, very severe headache, or sudden loss of vision

Contact your clinic if:

• Your thinking problems are getting steadily worse
• Fog is severe enough to affect your safety, work, or daily life
• It comes with new low mood, hopelessness, or thoughts of self-harm
• You have memory loss that is worsening or that others notice more than you do