Brain Fog and Chronic Illness: Why Your Brain Feels Slow, and What Actually Helps

🌫️ "Trying to think through molasses"

That's how researchers and patients alike describe brain fog in POTS, MCAS, hEDS and related conditions — reaching for a word mid-sentence, rereading the same paragraph three times, forgetting why you walked into a room. It isn't laziness, and it isn't "just tiredness." For a lot of spoonies, it's one of the most disruptive symptoms of all, and one of the hardest to explain to anyone who hasn't lived it.

🧠 POTS brain fog: what's actually happening in your brain

POTS brain fog is a documented cognitive symptom, not a vague complaint. In a 2015 study at Vanderbilt, 28 women with POTS and 24 matched healthy volunteers were given a battery of neuropsychological tests in a semi-recumbent position — that is, with orthostatic stress deliberately minimised. The POTS group scored significantly lower on selective attention, cognitive processing speed and executive function.

That detail about position is the important one. It means the fog isn't purely a consequence of standing up: it was measurable while sitting, when the heart rate problem was taken out of the picture.

Two honest caveats. Deficits in POTS are generally described as mild, with considerable overlap between patient and healthy scores — this is a real effect, not a dramatic one. And the pattern varies between studies: some measures, including memory and verbal fluency, showed no difference at all in that study.

One proposed mechanism involves chronic norepinephrine overload. A short adrenaline spike sharpens focus in an emergency, but sustained high levels — common in hyperadrenergic POTS — appear to interfere with the prefrontal cortex, the region responsible for executive function and working memory. A later study found that executive function scores while standing correlated negatively with plasma norepinephrine levels, which fits that picture. This is part of why brain fog can feel like being exhausted and wired at the same time.

It's worth saying that this matters beyond the biology. Being able to name the mechanism changes what happens in an appointment, and it changes what you tell yourself at 3pm when a simple email has taken forty minutes. The fog is not a measure of how hard you tried.

🔗 Want more like this? Browse all our POTS guides →

🔍 Find your own "brain fog thumbprint"

Brain fog triggers aren't identical from person to person. For some, it's clearly tied to standing, heat and dehydration. For others, poor sleep or a MCAS flare is the bigger driver. Tracking posture, hydration, sleep quality, heat exposure and brain fog severity together over a couple of weeks tends to reveal a pattern — clinicians sometimes call this your "thumbprint" — that's far more useful for troubleshooting than trying every strategy at once.

🌱 Strategies worth trying — and what the evidence actually shows

• 💧 Hydration. Increasing fluid intake is a standard first-line measure in POTS and is low-risk, so it's a reasonable starting point. Be aware that the evidence for it specifically improving cognition is thin — the strong case for fluids rests on orthostatic symptoms rather than brain fog.

• 😴 Sleep consistency. Going to bed and waking at roughly the same time, limiting screens before bed, and addressing pain earlier in the evening are commonly recommended for cognitive symptoms. If your sleep looks adequate on paper but never leaves you refreshed, non-restorative sleep may be the piece to look at.

• 🦵 Physical counter-manoeuvres — with a caveat worth knowing. Crossing your legs, clenching your fists or tensing your leg muscles while standing can help support blood pressure, and they're useful for orthostatic symptoms. But when leg crossing was actually tested against cognition, it did not improve executive function in POTS participants. So use them for the dizziness; don't expect them to clear the fog.

• 🐢 Pacing around known triggers. If heat, prolonged standing, or a big meal reliably brings on fog, scheduling demanding mental tasks away from those windows — rather than pushing through — tends to work better than fighting it in the moment.

🩺 When to loop in your doctor

Brain fog that's frequent, lasts for months, or starts interfering with work, school or daily responsibilities is worth raising directly with a healthcare provider — not something to just accept as part of the deal. A doctor can check for other contributing causes and, if early strategies aren't enough, may discuss options ranging from addressing underlying hypovolemia to targeted medication, always as part of an individualised plan.

❓ Frequently asked questions

📚 Sources & further reading

The information in this article is drawn from the following sources. We encourage you to explore them.

• Arnold AC, Haman K, Garland EM, et al. — Cognitive dysfunction in postural tachycardia syndrome. Clin Sci (Lond). 2015;128(1):39–45.

• POTSKog study — Cognitive functioning in postural orthostatic tachycardia syndrome among different body positions (leg crossing and executive function)

• Dysautonomia International — Cognitive Dysfunction and "Brain Fog" in POTS

• PoTS UK — Cognitive Dysfunction or "Brain Fog" in PoTS