Stand up, and the supply drops.
When you stand, brain blood flow drops about seventeen seconds before the heart speeds up and the adrenaline hits, so the racing heart is the reaction, not the cause. POTS, long COVID, ME/CFS and hypermobility all run on that same upright-flow drop, and for many it can be rebuilt.
The drop comes before the racing heart.
Standing drops your brain’s blood supply twice as far as it should, and that flow gap, not anxiety, is what feels like panic.
Stand up, and brain blood flow drops roughly twice as far as it should, often without any meaningful fall in blood pressure, about 20 percent versus 10 percent in healthy people.1 The shortfall arrives about seventeen seconds before the heart races and the adrenaline surges, which puts low perfusion first in the chain rather than as a reaction to it.2 The brain compensates by breathing harder, which blows off CO2 and tightens its own vessels, deepening the shortfall: a self-reinforcing loop that reads, from the inside, like panic.
One shared mechanism, four names. POTS, long COVID, ME/CFS and hypermobility all run on the same upright-flow drop, which is why they travel together and answer to the same toolkit. They are not one disease: each carries its own verdict, and one head-to-head study reads them as overlapping but distinct. And most of these patients are told it is anxiety before the cause is found.3
Add up what you are working against.
Your starting brain blood flow is the sum of everything draining it, standing included. Open the meter, tick what applies, and watch the margin you have left, then see what each substance costs you.
Tap how many times you have had COVID, if any, then tick anything else that fits. This adds up one thing only, resting brain blood flow measured in imaging studies, not worth or blame. An ADHD or autistic brain is counted because it is perfused differently, not because it is a flaw. This is the trait itself, separate from prescribed ADHD medicine, which is a treatment that does not drain flow.
The per-factor figures come from brain-imaging studies and are sized conservatively, with the full sourcing below. The top bar stacks the resting blood-flow each factor costs, each one taken from the flow still left; the second runs higher because the brain has so little spare flow to spend that the cost to thinking outruns the raw drop in supply.
Where these come from
We sized each factor by how much it lowers resting cerebral blood flow in brain-imaging studies (ASL-MRI, SPECT, PET). Most are small on their own, and several are regional or only show up under stress. Where a finding is regional, we enter a reduced whole-brain-equivalent share rather than the larger regional figure. The sources:
- COVID: regional rather than whole-brain,4 so it stacks roughly with each infection; each one also carries an IQ-equivalent cost.5
- Smoking or vaping: lowers resting flow, though acute nicotine briefly pushes it the other way.6
- An ADHD brain, concentrated in the frontal regions.7
- Artery plaque or vessel disease: narrowing throttles the supply to the regions it feeds, and even silent plaque lowers flow.8
- Autism: concentrated in temporal and frontal regions; the whole-brain average reads normal, so we enter only a reduced whole-brain-equivalent of that regional shortfall.9
- Chronic inflammation: corrodes the vessel lining and the flow-matching system; higher long-term markers track a faster loss of regional flow.10
- Lower lung oxygen: small, because the brain widens its vessels to compensate.11
- Chronic poor sleep: clearest in sleep apnea.12
- POTS: close to normal at rest, with a sharp, temporary drop when you stand.1
Anxiety has no steady whole-brain percentage in this list: it shows a regional pattern rather than one number, and its sharpest forms, panic and standing, are already counted above through POTS.13 Anxiety has its own page.
For most, the flow comes back.
Start without drugs: more fluid and salt if your blood pressure, heart and kidneys allow, waist-high compression, and a recumbent-first exercise rebuild on a rower, a recumbent bike or in a pool. One rule that is not optional: screen for post-exertional malaise first. If you crash a day or two after overdoing it, that is post-exertional malaise, and push-through exercise can do lasting harm, so pace within your limits and rebuild in tiny steps. Most people who complete that programme stop meeting the criteria for POTS.14 If that is not enough, drugs matched to your pattern come next with a clinician: ivabradine or low-dose propranolol to slow the racing heart, midodrine, droxidopa or fludrocortisone for pooling and low standing pressure. The full toolkit, sleep, breathing, heat and diet, is on What helps.
Four names, one mechanism.
Each runs on the upright-flow drop above, and each carries its own verdict and evidence. They overlap heavily, and many people sit in more than one.
POTS and dysautonomia strong, mechanicalflow crashes on standing; refill the tank
That upright-flow drop above is POTS.1 Breathing speeds up to compensate, which strips out CO2 and clamps the brain's own vessels, so the shortfall deepens, a self-reinforcing loop that, with the adrenaline-and-racing-heart response, is a leading explanation for the brain fog and panic on standing.2 The flow drop is well measured, but whether it directly causes the symptoms is debated, which is why treatment works upstream, restoring upright blood volume with salt, fluids and compression.15 Why some people pool more is partly structural: laxer vessel walls, as in hypermobility, distend further under the same standing pressure, one reason connective-tissue laxity travels so closely with POTS.16
Long COVID and brain fog big studies, debated causea real cognitive hit; the mechanism stays debated
The largest study, in nearly 113,000 people, found a loss on the order of six IQ-equivalent points in those with unresolved symptoms.5 ASL-MRI and PET independently show drops in blood flow and metabolism in orbitofrontal, limbic and brainstem regions, and the leading explanation for brain fog is dynamic neurovascular failure: small-vessel and endothelial dysfunction with a leaky blood-brain barrier, often worse when flow falls on standing. Around 92 percent of patients in these clinic cohorts show reduced upright cerebral blood-flow velocity even when heart rate and blood pressure look normal, a pattern shared with ME/CFS.171819 The microclot theory is plausible but contested, and no independent cohort has confirmed it.20
ME/CFS, chronic fatigue strong when uprightpace, never push through; exertion crashes you
Stand someone with ME/CFS upright and their brain blood flow drops about 26 percent, versus 7 percent in healthy people, measured by ultrasound of the neck arteries. That large drop shows up even in patients whose heart rate and blood pressure look normal, the ones a standard POTS workup misses, and in that group the flow did not fully recover on lying down, with the sicker patients showing the larger drops, though this is a single-group finding the recent systematic review still treats as unsettled.21 Long COVID produces the same orthostatic signature, a reason the two illnesses are seen as overlapping, though the samples are small.22 Much of this work, including the long-COVID and hypermobility comparisons, comes from one research group using its own neck-artery method, so it is repeated extension rather than independent replication, and whether the low flow is a root cause or a downstream consequence remains unproven.23 One safety point specific to this group: the defining feature is post-exertional malaise, a delayed crash after exertion, and push-through exercise can do lasting harm, so pace within your limits rather than train through it.
Hypermobility and connective tissue (hEDS/HSD) strong link, debated causeloose joints travel with standing blood-flow trouble
Loose joints often come with a loose circulation. In hypermobile Ehlers-Danlos syndrome and the wider hypermobility spectrum, the same lax connective tissue that lets joints overextend is thought to let leg and abdominal veins stretch and pool more blood when you stand, which is one proposed reason this group leans so heavily toward POTS and orthostatic intolerance.16 The association is real and runs both ways: across hypermobility clinics orthostatic intolerance runs around 74 percent versus 34 percent in controls, roughly half of POTS patients fall somewhere on the hypermobility spectrum, and in the largest hEDS cohort 79 percent showed reduced brain blood flow on standing.242526 Measured by ultrasound of the neck arteries, ME/CFS patients who are hypermobile drop their cerebral blood flow about 32 percent on tilt versus 23 percent in those without hypermobility, even when heart rate and blood pressure look normal.27
The catch is the mechanism. Hypermobile EDS has no identified gene and no demonstrated vessel-wall defect, the extra pooling is mostly inferred rather than measured in hypermobility itself, and the autonomic testing points as much to a small-fibre, sympathetic neuropathy as to slack veins.26 Most of these numbers also come from specialist clinics; at the community level hypermobile children show no clear excess of POTS, so referral bias inflates the clinic picture.28 This group shares the upright-flow signature of long COVID and ME/CFS, though one head-to-head study reads them as overlapping but distinct.19 The same orthostatic toolkit applies: salt, fluids, compression and recumbent-first reconditioning. One caution matters most here. This is the common hypermobile type, with vessel walls thought to be more distensible, diagnosed in about 1 in 500 people and skewing female.29 Do not confuse it with vascular EDS, a separate, rare disease caused by COL3A1 mutations that ruptures arteries and organs and needs specialist surveillance.30
Fibromyalgia real signal, not a causethe nervous system cranks up pain itself
Fibromyalgia is a real disorder of central pain processing, not all in your head. The mainstream model is central sensitization, also called nociplastic pain: the nervous system amplifies pain and loses its built-in dampening, with no tissue damage to point to. There is a genuine brain-imaging literature, SPECT shows altered regional flow that tracks disability,31 and perfusion-MRI shows the thalamus uncoupling from the pain network,32 but the studies are small and the changes look like markers of amplified processing, not a blood-starvation cause. About half of patients also show small-fiber nerve changes on skin biopsy, so the periphery matters too. The old psychogenic label is outdated. Diagnosis is clinical, not imaging-based; a clinician can guide treatment.
Chiari changes the drainage, not the delivery.
A Chiari malformation, where the lower tip of the cerebellum hangs below the base of the skull, does measurably change the brain’s blood flow, but on the drainage side, not the supply side. In symptomatic Chiari, blood leaves the head less through the jugular veins and more through cramped collateral routes, the venous pulsation is smaller, and this partly reverses after surgery to open up the space.33 The skull’s pressure-buffering capacity runs about a fifth lower than in healthy people,34 and narrowing of the large draining sinuses is far more common.35
What that is not, on the evidence, is less blood delivered to the brain. The arterial inflow measured in Chiari is normal,33 and no perfusion scan, the kind that would show brain tissue actually running short, has tested it either way. So the honest line is narrow: Chiari alters cerebral venous outflow and the pressure buffer around the brain, a real abnormality on the outflow side, but it has not been shown to starve the tissue, and it has not been shown to cause POTS or brain fog through low flow. In the one controlled comparison, people with orthostatic intolerance had cerebellar tonsils sitting at perfectly normal levels.36
It helps to know how often the label turns up without the disease. A small dip of the tonsils past the five-millimetre line is a common incidental finding in people with no symptoms at all, and expert readers measuring the same scans disagree by several millimetres.3738 International guidance is not to operate on a Chiari found by chance, with no fluid cavity in the cord and no symptoms.39 A radiology line reading Chiari is far more often an anatomical variant than an explanation, and it is a different thing from the chiropractic idea of a ‘misaligned atlas’, which is not a recognised cause of any of this and has no controlled evidence behind it.
A genuinely symptomatic Chiari is a real minority, and it has a signature worth knowing on sight: a short, stabbing headache at the back of the head brought on by coughing, laughing or straining; a syrinx, a fluid-filled cavity in the spinal cord; or new brainstem, balance, swallowing or limb signs. Those features, not the millimetres on the scan, are the reason to get imaging and a neurosurgical opinion. This is information, not a diagnosis: if that pattern fits you, have it looked at properly.
Standing trouble is read as anxiety more often than almost anything else, see when the body is the cause. If you actually black out rather than just feel woozy, see fainting, and since low iron is common in this group, anemia if you are tired and pale too. If yours began after an infection, see what COVID does to the vessels; after a head injury, see concussion and TBI. And what helps for the full toolkit.
Keep your brain better supplied.
Most research on cerebral blood flow stays locked in journals, behind paywalls and jargon, far from the people it could help. The newsletter reads it for you and sends only what changes what you can do: a new way to raise your own blood flow, or a finding that moves the advice on this page.
The list is not open yet. It opens with the first issue. A few emails a year, every claim sourced.