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.

What's actually happening in your brain

Research on POTS specifically has found measurable deficits in selective attention, processing speed, and executive function — and, notably, these show up even while seated, not just when standing. That's a meaningful finding: it suggests brain fog isn't purely a side effect of reduced blood flow to the brain on standing, but may be part of the condition itself in some patients.

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 brain region responsible for executive function and working memory. This is part of why brain fog can feel like being exhausted and wired at the same time: physically drained from reduced blood flow, but neurologically overstimulated from excess adrenaline.

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 with some evidence behind them

• Hydration. A small study on neuropathic POTS found that drinking water measurably improved both cognitive function and orthostatic symptoms — one of the simplest, lowest-risk interventions with actual data behind it.

• Sleep consistency. Going to bed and waking at roughly the same time, limiting screens before bed, and addressing pain earlier in the evening are consistently cited as some of the highest-return changes for cognitive symptoms.

• Physical counter-maneuvers. Simple movements like crossing your legs, clenching your fists, or tensing your leg muscles while standing can help maintain blood pressure and may ease brain fog for people with milder symptoms.

• 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.

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

• RTHM — Brain Fog in POTS: How Reduced Cerebral Blood Flow Clouds Your Thinking

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