Brain Fog Causes: Why It Gets Worse When You Stand or Drive

What Is Brain Fog?

Brain fog describes how thinking feels, so it doesn't have a strict medical definition. In a survey of 138 young people with POTS, 96% reported brain fog, and the words they picked most were forgetful, difficulty thinking, difficulty focusing, cloudy and trouble finding the right words (Ross, 2013). Our team uses it to mean cognitive inefficiency: you try to think at your normal level, and it doesn't come through, or it tires you out far more than it should.

Our team uses a football stadium doing the wave as a picture of it: a thought needs large groups of brain cells working in sync, the way a whole stadium has to stand up on cue for the wave to travel around it. If 10 people stand and the rest stay seated, the wave dies. In our team's view, when groups of brain cells don't have the energy to keep up, they fall out of sync, and a thought starts, fizzles out and has to start over. That's the looping, half-finished thinking many people describe.

What Causes Brain Fog?

Brain cells need oxygen and glucose to work, and they need more of both the moment you ask them to do something. Our team checks the supply chain in order, because a break anywhere along it shows up as the same fog:

• Sleep. Sleep is when the brain restores itself. In healthy people, staying awake for up to 48 hours caused lapses in simple attention (Lim, 2010), and lack of sleep was among the top triggers of brain fog in the POTS survey, named by 90% (Ross, 2013). Our team sorts out sleep first, because nothing downstream works well without it.
• Fuel in the blood. If the blood carries less oxygen or glucose, less reaches the brain. In a 16-week trial of iron or placebo in women aged 18 to 35, a bigger rise in iron stores (ferritin) went with better scores on thinking tasks (Murray-Kolb, 2007). In a lab study that lowered blood sugar on purpose to about 50 mg/dL, well below normal, reactions slowed and working memory errors rose in adults with or without diabetes (Verhulst, 2022).
• Blood into the brain. Some people make enough fuel but can't deliver enough blood to the brain, especially upright. This is called cerebral hypoperfusion, and in our team's experience it's the layer most often involved in POTS and other forms of orthostatic intolerance.
• Brain cells using the supply. Brain activity and blood flow are closely linked in time and place, a link called neurovascular coupling (Phillips, 2016). After a sport concussion, that response was altered on transcranial Doppler testing (Wright, 2017). Our team pays close attention to this link in people whose recovery after a concussion or a viral illness has stalled.

Being sick can do it too: infection and inflammation can make memory and learning harder (Dantzer, 2008), and in an online survey of 3,762 people recruited through long COVID support groups, 85% reported brain fog and cognitive dysfunction (Davis, 2021). Our team also looks for a past brain injury, problems with the lining of the blood vessels, and narrowing in the neck vessels that carry blood to the brain. Whatever the cause, our team treats what's behind the fog, because the fog itself is the signal that something upstream is short.

Why Is Brain Fog Worse When You Stand?

Lying down, your brain gets an easy supply: the heart doesn't have to push blood uphill. Standing, gravity pulls blood down toward your legs, and in our team's view, that's where the trouble starts for many people with POTS: the body has to work to keep enough blood flowing to the head. In the POTS survey, 87% named prolonged standing as a brain fog trigger and 86% named dehydration, and lying down was the most common thing that helped, named by 81% (Ross, 2013). In 1 study, people with chronic fatigue syndrome and POTS kept up with healthy people on a working memory test lying flat, then fell behind as the table was raised to 45 degrees and higher (Ocon, 2012).

Standing doesn't explain all of it. In that tilt study, blood flow velocity to the brain fell about as much in the healthy group, so it didn't explain the drop in thinking performance (Ocon, 2012). In the survey, fog was reported to persist after lying down, and lack of sleep still triggered it lying flat for 70% (Ross, 2013). Because flow at rest doesn't tell the whole story, our team also tests how blood flow responds to thinking itself.

If your fog is fine lying down and goes through the roof upright, our team looks first at whether blood is reaching your brain when you stand.

Why Do I Get Brain Fog While Driving?

No study has looked at brain fog while driving in people with POTS, so what follows is our team's reasoning from the supply chain above. Driving stacks 3 demands on a brain that may already be short on supply:

• A long stretch upright with your legs still. Sitting asks less of your circulation than standing, but fog doesn't need you on your feet: 28 women with POTS, tested semi-reclined, scored lower than 24 healthy women on selective attention, processing speed and executive function, while sustained attention, psychomotor speed and memory held up (Arnold, 2015). In our team's reasoning, a long drive with little leg movement gives your leg muscles little chance to help push blood back up.
• Moving scenes. Traffic and passing scenery keep your eyes and balance system tracking motion. Some people with balance disorders find their dizziness provoked by driving and other busy visual scenes (Guerraz, 2001), and the criteria for persistent postural-perceptual dizziness list moving visual scenes, like passing traffic on a highway, as a trigger (Staab, 2017). Neither study looked at brain fog.
• Steady attention. Driving asks your brain to keep taking in new information, and in the POTS survey, 81% said prolonged concentration triggered their fog (Ross, 2013). In our team's view, when capacity is low, one demand can use it up and the next one falls behind.

If fog, drowsiness or lightheadedness comes on while you're driving, pull over somewhere safe. If it happens often, talk with your clinician about whether to drive while you work out the cause. When fog shows up mainly while driving, our team checks the same 2 places it checks for fog on standing and in busy scenes: blood flow to the brain upright and how your brain handles visual motion.

Is Brain Fog Part of POTS?

Brain fog is one of the most common symptoms of POTS: 96% of the 138 young people in the online survey above (Ross, 2013), and 3,794 of 4,032 respondents (94%) in a larger online survey of people with POTS reported difficulty concentrating (Shaw, 2019). The diagnosis itself rests on the heart rate rise when you stand, measured with a tilt table test or a standing test. In our team's view, POTS care often stays centered on the heart, since the name has tachycardia in it and the main test watches heart rate, while fog, stomach and sleep problems get sent to separate specialists.

Our team sees them as outputs of the same upstream problem. The autonomic nervous system runs the heart, blood vessels, breathing and gut at the same time. Our team sees the fast heart rate on standing as a compensation, the heart speeding up to keep blood reaching the brain, and fog as what shows when that compensation can't fully cover the shortfall. Medicines can help and can serve as a bridge. In our team's view, their ceiling is that they act on heart rate, blood volume or vessel tone without retraining how the brain holds its own blood flow steady. When fog persists on them, our team looks upstream at how the brain is managing blood flow as well as at the heart.

How Do You Find the Cause of Brain Fog?

Fog that comes on suddenly with weakness, numbness, trouble speaking, trouble seeing or a sudden severe headache can be a stroke: call 911 right away (MedlinePlus). For fog that builds over weeks or months, our team sets the fog aside for a moment and looks at what comes with it, because in our team's experience the combination points to the mechanism:

• Fog with dizziness on standing or headaches that change with position points toward blood flow to the brain.
• Fog with light sensitivity and trouble with busy or moving scenes points toward vestibular or cerebellar dysfunction.
• Fog with fatigue and getting sick often points toward inflammation or the immune system.

Testing follows the supply chain. Basic labs can check blood sugar and iron. A tilt table test with a transcranial Doppler shows whether blood flow to your brain holds up when you're upright. Our team then adds thinking tasks, like math problems or listing words that start with a letter, to see whether blood flow keeps up with the demand. In 1 small study of 22 people with POTS and 18 healthy people, a 30-minute thinking task done while seated lowered blood flow velocity to the brain more in POTS, 7.8% against 1.8%, down to the level seen when they stood, and slowed their responses (Wells, 2020).

How Is Brain Fog Treated?

Treatment depends on which link is weak. Sleep problems get sorted out first, and fuel problems, like low blood sugar or low iron, get checked and addressed. When blood flow to the brain drops upright, our team works on the systems that should hold it steady: the squeeze in your vessels, blood return from your legs, your breathing and CO2, and the brain's own flow control. When brain cells aren't drawing on the supply the way they should, our team uses neurorehabilitation that activates those cells, so the link gets stronger with use. In each case the goal is for the fog to lift as the supply chain is repaired.

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