What to explain
Show what happens to your symptoms, heart rate, and blood pressure when you stand.
Use the parts that match your experience.
My thinking becomes harder after [standing up / staying upright for a while]. I also notice [symptoms that apply]. After I sit or lie down, [what happens]. Could we compare my symptoms with blood pressure and heart rate while lying and standing, then decide what to check next?
Questions to take in
Ask which standing-related condition fits and which other causes need checking.
- When I felt faint or muddled, did my blood pressure fall, heart rate rise, or heart rhythm change enough to explain it?
- Do the results fit orthostatic hypotension, POTS, a fainting reflex, a heart rhythm problem, or another explanation?
- Could dehydration, bleeding, anemia, thyroid disease, infection, diabetes, a nerve condition, long bed rest, or a medicine explain the result?
- Is an office standing test enough, or would a longer active stand, tilt table test, ECG monitor, or specialist assessment answer a clear question?
- Which steps are safe for me while we investigate? Should I change fluids, salt, meal size, compression clothing, exercise, or any medicine?
- Do any of these apply to me and change the advice: high blood pressure, a heart condition, kidney disease, pregnancy, older age or a risk of falling?
- If blood pressure and heart rate don't explain the brain fog, which cause should we check next?
- Should I see cardiology, neurology, an autonomic clinic, physical therapy, or another service, and what question should that referral answer?
Lying and standing circulation checks
Standing measurements, heart checks, and blood tests for symptoms that worsen upright.
Standing blood pressure and pulse are the usual starting point. A longer stand or tilt test may answer a specific fainting or POTS question. Blood tests and medicine review look for dehydration, anemia, low iron, thyroid disease, glucose or electrolyte changes, and other causes.
Orthostatic Vital Signs and Active Stand Test
Measures blood pressure, heart rate, and symptoms while lying down and after standing. A sustained drop of at least 20 mm Hg systolic or 10 mm Hg diastolic within 3 minutes meets the usual orthostatic-hypotension definition.
Read the test guideNASA Lean Test
Records heart rate, blood pressure, and symptoms during a supported 10-minute stand. It can collect useful information but does not diagnose POTS or prove low brain blood flow by itself.
Read the test guideTilt Table Test
Monitors heart rhythm, heart rate, blood pressure, symptoms, and recovery while a secured table moves the body upright. It is chosen when the history and initial assessment leave a clear fainting or standing question.
Read the test guideCBC + CMP Blood Test Bundle
The CBC can show anemia. The CMP can show glucose, electrolytes, kidney, liver, and protein results that may identify another reason for low pressure, a fast pulse, weakness, or brain fog.
Read the test guideFerritin
Estimates stored iron. Low iron can exist with or without anemia, while inflammation can raise ferritin. The result needs the blood count, symptoms, bleeding history, and laboratory range.
Read the test guideTSH
Checks thyroid control. An overactive thyroid can raise heart rate, while an underactive thyroid can cause fatigue and thinking trouble. The result does not measure brain blood flow.
Read the test guideMedication Review
Checks whether a prescription, over-the-counter medicine, supplement, dose, or interaction may lower blood pressure, reduce fluid volume, raise heart rate, cause sleepiness, or worsen balance.
Read the test guideBefore the appointment
Bring the position, timing, symptoms, readings, medicines, and earlier results.
Describe one usual episode: what you were doing, how long you had been upright, what changed in your thinking or vision, and what happened after you sat or lay down. You don't need to bring on another episode or keep a new week-long diary for the appointment.
Bring any blood-pressure or pulse readings you already have. If you know, include each reading's time, which arm and cuff you used, and whether someone was nearby. Skip repeating a standing test just to get more numbers.
Describe any faint or near-faint in detail. Include warning symptoms, injury, movements, loss of bladder control, how long you were unresponsive, and how you felt afterward. Bring a witness account when available.
Bring every prescription, over-the-counter medicine, and supplement, plus earlier ECGs, heart-monitor reports, blood tests, emergency notes, and tilt or standing-test reports you already have.
Mention any recent fever, infection, vomiting, diarrhea, heavy sweating, heavy menstrual bleeding, black or bloody stool, surgery, long bed rest, pregnancy, or a change in eating and drinking.
Say whether heat, showers, meals, exercise, a menstrual period, or a long time standing changes the symptoms. Also mention relevant heart, kidney, blood, thyroid, neurological, migraine, long COVID, ME/CFS, or hypermobility history.
A heart-rate or blood-pressure result is easier to understand when the doctor knows what you felt at that time.
How the doctor assesses this
Signs that standing may be part of the problem
- Brain fog, dizziness, dim vision, weakness, nausea, or heart racing begins after standing.
- Sitting or lying down helps more quickly than simply waiting while upright.
- The usual symptoms happen while readings show blood pressure dropping, heart rate rising, or another standing response.
Signs that another cause may need checking
- Brain fog is the same while lying down, sitting, and standing, and there is no dizziness, dim vision, weakness, nausea, racing heart, near-fainting, or relief after lying down.
- Carefully repeated standing checks do not bring on the usual symptoms and do not show a blood-pressure or heart-rate change that explains them.
- Brain fog follows poor sleep, a meal-related glucose change, migraine, a seizure, a medicine dose, low mood, anxiety, infection, or another cause more closely than it follows standing.
- Fever, pain, dehydration, bleeding, anemia, a stimulant, or recent long bed rest explains a temporary heart-rate rise. That does not meet the full requirements for POTS.
- Sudden trouble speaking, one-sided weakness, a new severe headache, or a seizure points to a neurological emergency, not a routine standing check.
What to understand before choosing care
What the doctor should check before calling this low brain blood flow.
- Hypoperfusion means lower blood flow. A home blood-pressure cuff measures arm pressure, not blood flow inside the brain.
- Please compare my symptoms with blood pressure and heart rate from the same minutes. A number without the matching symptom time can be misleading.
- A blood-pressure drop when standing, POTS, a fainting reflex, and a heart rhythm problem are different findings. Please tell me which one the results support.
- Please check medicines, hydration, bleeding, anemia, thyroid disease, infection, heart problems, and other causes before naming a long-term autonomic condition.
- I will not greatly increase salt or fluid, use compression clothing, stop a medicine, or begin an exercise program on my own. A clinician should first check my blood pressure, heart, kidneys, pregnancy status, and other conditions.
What the research found
What recent studies found about brain blood flow and POTS.
Blood pressure and heart rate at the arm do not directly measure blood flow inside the brain. They help identify a standing-related circulation problem that may need further assessment.
A 2025 study looked back at the records of 56 selected people who had POTS, thinking problems and brain SPECT scans. SPECT shows blood flow in different brain regions. Thirty-four people, or 61%, had at least one region with an abnormal result. All came from one clinic. The study had no comparison group chosen to match their characteristics, so it does not support routine SPECT scans for everyone with brain fog.
A 2020 study compared 22 people with POTS with 18 healthy controls. The POTS group had slower thinking after a 30-minute seated mental task, along with changes in middle-cerebral-artery flow velocity. It was a small study and cannot show that low flow explains every POTS symptom.
A separate 2020 study of 11 people with POTS and 8 controls found thinking differences even though seated cerebral blood-flow measures were similar. Research does not support treating every case of POTS brain fog as one simple blood-flow problem.
A 2026 study compared 18 people with POTS with 20 matched controls. The POTS group was slower on tests of executive function, which includes planning and controlling attention. They also had lower blood flow in some brain areas during tests of automatic nerve responses. This early, small study may help explain what happens in POTS. It is not a diagnostic test for an individual person.
Age, sex and pregnancy
For a child or teenager, use a pediatric clinician and a safe supervised standing test. For people aged 12 to 19, the POTS criteria use a heart-rate rise of at least 40 beats per minute, not the adult 30-beat cutoff.
POTS is reported most often in teenage girls and young adult women, but it can affect boys, men, older adults, and people of any background. Sex or age alone cannot make the diagnosis.
A menstrual period can worsen upright symptoms in some people. Mention the timing, but check blood loss, anemia, migraine, medicines, and other explanations before assuming hormones are the cause.
Orthostatic hypotension becomes more common with age. In an older adult, medicine effects, falls, dehydration, diabetes, Parkinson disease, heart disease, and high blood pressure need particular attention.
Pregnancy can change blood pressure and circulation. Fainting, bleeding, severe vomiting, chest pain, breathlessness, or new neurological symptoms need prompt medical advice. Ask your pregnancy care team before increasing salt, fluid, or medicines.
If the answer is no
If your doctor will not order a brain perfusion scan
Brain blood-flow imaging is not a general test for brain fog. NINDS says doctors use your history and nerve and brain exam to choose blood tests, MRI, spinal-fluid tests, PET, SPECT, or another test. If standing brings on symptoms, heart rate and blood pressure while lying and standing may be a better first check.
What changes the answer
- Lead with the position change. Say whether symptoms begin after standing, improve on lying down, occur with heat or meals, and include dizziness, dim vision, a racing heart, or near-fainting. These details guide the first exam.
- Ask for lying and standing measurements. Blood pressure and pulse recorded after rest and again while standing can document an orthostatic change. Bring home observations as context, but ask for a properly recorded clinical set.
- Ask what finding would justify imaging. A neurological examination can identify weakness, sensory change, balance problems, speech changes or other signs that move the question toward MRI or another targeted test.
- Ask what else could cause the symptoms. If standing measurements are normal, ask whether sleep, anemia, medicines, migraine, balance problems, or a neurological condition could explain the symptoms. A normal bedside test doesn't prove the symptoms aren't real.
United States, United Kingdom, and Australia
Who to contact about Brain Fog When Standing.
US United States
Ask primary care to measure the standing response. Bring the symptom and position notes. Primary care can repeat the measurements, check common causes, and decide whether you need a rhythm monitor, tilt test, or specialist referral.
- Primary care can compare symptoms with blood pressure and pulse after 5 minutes lying down and after 1 and 3 minutes standing.
- The clinician should record symptoms beside each lying and standing reading, then review possible triggers, medicines, dehydration, anemia, and other causes before choosing treatment.
- The clinician should check what brings on the symptoms and review your medicines. Any treatment must also be safe for high blood pressure and your other conditions.
UK United Kingdom
Ask the GP to compare symptoms with standing measurements. The GP can check blood pressure and heart rate, arrange selected blood tests and an ECG, and refer when the result or severity needs specialist assessment.
- A GP may check blood pressure and heart rate before and after standing and repeat the measurements as an active stand test.
- Blood tests may find anemia, low glucose, or an electrolyte problem. An ECG may find an abnormal heart rhythm.
- Specialist tests may be used when symptoms are severe, the cause remains unclear, or initial changes do not help.
AU Australia
Ask the GP to check blood pressure, pulse, and common causes. A GP can repeat lying and standing measurements, order selected tests, review medicines, and refer to a specialist when fainting, abnormal results, or ongoing symptoms need more assessment.
- A GP may measure blood pressure and heart rate while you are lying down and standing.
- Medicines, dehydration, anemia, pregnancy, heart disease, diabetes, nerve problems, and other causes may need checking.
- Treatment depends on the cause. Salt, fluids, compression, exercise, or medicine changes need advice that fits the person's other health conditions.
Safety
Stay safe during everyday activities
- Set up ordinary upright activities so you can sit quickly. Use a shower seat, prepare food at a table, and sit while waiting in line when fainting is possible.
- If you become lightheaded, sit or lie down safely. Skip driving, ladders, swimming alone, hot baths, or anything else where a faint could cause injury until the cause is assessed.
- Keep normal, regular food and fluid intake unless a clinician has given you a restriction. Skip using large salt doses or extreme water intake to diagnose yourself at home.
- Include heat, meals, illness, sleep, alcohol, caffeine, exercise, and menstrual timing when any of them coincides with the standing symptoms. This helps the doctor choose which cause to check.
- After a clinician chooses a safe step, change one thing at a time and compare the same daily activity. This makes any functional change easier to interpret.
Source checked
Sources behind this handout.
- 01
Centers for Disease Control and Prevention. Measuring Orthostatic Blood Pressure.
Source - 02
Juraschek SP et al. Orthostatic Hypotension in Adults With Hypertension. American Heart Association Scientific Statement. Hypertension. 2024;81:e16-e30. PMID 38205630.
Source - 03
Vernino S et al. Postural Orthostatic Tachycardia Syndrome: State of the Science and Clinical Care From an NIH Expert Consensus Meeting. Auton Neurosci. 2021;235:102828. PMID 34144933.
Source - 04
Seeley MC et al. Novel Brain SPECT Imaging in POTS and Cognitive Dysfunction. Sci Rep. 2025;15:3487. PMID 39875497.
Source - 05
Wells R et al. Cerebral Blood Flow and Cognitive Performance in POTS. J Am Heart Assoc. 2020;9:e017861. PMID 33280488.
Source - 06
Malik V et al. Brain Tissue Changes, Network Dysfunction, and Cerebral Hemodynamic Deficits in POTS. Heart Rhythm. 2026. PMID 41740821.
Source