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Published 31 August 2026

Why you feel dizzy when you stand up

You get off the sofa and the room goes grey at the edges. Sound gets distant. You put a hand on the doorframe and wait for it to pass. Almost everyone has had a version of this. For some people it happens every single time they stand, and that is a different thing worth understanding.

Gravity gets a vote

When you are lying down, your blood is spread more or less evenly along the length of you. Stand up and gravity pulls a meaningful volume of it downwards, into the veins of your legs, pelvis and abdomen. Veins are stretchy — that is their job — so they accept it happily. Which is fine for your legs and inconvenient for your brain, because the blood that pools below is blood that is not coming back to your heart to be pumped upward.

For a second or two, the amount of blood filling your heart between beats drops. Less filling means less volume pushed out per beat. Less volume pushed out means blood pressure at the level of your head starts to fall. Your brain has an extremely short tolerance for this: consciousness depends on a steady supply, and the reserve is measured in seconds, not minutes.

So your body has a reflex for it, and it is fast.

The ten-second correction

Pressure sensors in the walls of your carotid arteries and aorta — baroreceptors — notice the drop almost immediately. They report it upward, and the autonomic nervous system, the part that runs your body without asking you, responds on two fronts at once.

First it squeezes. Blood vessels in your legs and abdomen constrict, pushing the pooled blood back toward the centre. Second it speeds up. Heart rate rises, so even if each beat carries slightly less, more beats per minute keeps the total flow up. Together these two moves are supposed to catch the falling pressure within a few seconds and hold it steady, and you notice nothing at all.

The head-rush most people occasionally get is that correction arriving a beat late — usually after a hot shower, a long lie-in, a fast stand from a deep squat, or a day of not drinking enough. The grey edges are your visual cortex, which is fussy about blood supply, briefly running short. It resolves in a few seconds and you carry on.

When the correction does not work cleanly

There are a few different ways the reflex can underperform, and they feel different from each other.

The squeeze is weak. If your blood vessels do not constrict enough, blood keeps pooling low. Your blood pressure falls on standing and stays down. This tends to feel like heaviness, greying vision and a strong need to sit, and it typically shows up as a drop in blood pressure when it is measured.

The volume is low. If there is simply less blood and fluid in circulation — dehydration is the everyday version — there is less to work with and every stand costs more. This is why symptoms are often worse first thing in the morning, in hot weather, after illness, and after a night of poor sleep.

The heart rate compensates hard, and keeps compensating. Here the pressure is defended, but at a price: the heart runs fast the entire time you are upright and never settles. This is the pattern that people mean when they talk about postural orthostatic tachycardia syndrome, or POTS. The tell is not a single fast reading — it is a sustained rise that persists over minutes of standing rather than settling after the first few beats.

The reflex overshoots and then quits. In a simple faint, the body compensates and then abruptly reverses: heart rate and blood pressure fall together and you go down. Fainting is common, usually benign, and still worth telling a doctor about, because it should be looked at rather than assumed.

Why it is called orthostatic intolerance

“Orthostatic” just means upright. “Orthostatic intolerance” is the umbrella term for symptoms that appear when you are upright and are relieved when you lie down. That relief-on-lying-down part is the useful bit of the definition, because it separates this from the many other reasons a person can feel unwell.

The symptoms go far past dizziness, which is why it takes people so long to connect them. Common ones include lightheadedness, greying or tunnelling vision, a pounding or racing heartbeat, breathlessness out of proportion to the effort, brain fog that arrives after a few minutes of standing, nausea, shakiness, headache, sweating or its absence, blotchy purple-red legs after standing still, and a wave of exhaustion afterwards that can last hours. Standing in a queue is often worse than walking, because walking makes your calf muscles pump blood back up and standing still does not.

The things that make any of this worse

Whatever the underlying reason, the same levers move the needle: heat, dehydration, alcohol, big carbohydrate-heavy meals (digestion diverts blood to the gut), the days around a period, illness, and any long stretch of lying down or bed rest, which quickly makes the reflex lazier. Standing still, hot showers, and standing up quickly from a bath are the classic triggers people learn to respect.

When to get this looked at

An occasional head-rush after jumping off the sofa is ordinary. Get evaluated by a clinician if the dizziness happens most times you stand, if it is getting worse, if it limits what you can do in a day, if you actually faint or come close to it, or if it comes with chest pain, palpitations that frighten you, or breathlessness. Sudden or severe symptoms deserve urgent care rather than a wait-and-see.

Bring specifics. “I get dizzy sometimes” is hard to act on. “It happens within two minutes of standing, most mornings, and lying down fixes it in about a minute” is a description a clinician can work with. There are several possible explanations for orthostatic symptoms, some of them unrelated to the autonomic nervous system entirely, and sorting between them is a job for a real examination — not a phone, and not an article.

What you can do in the meantime

You can gather evidence. The single most useful thing most people bring to a first appointment is a record: what happened, when, how long you had been upright, and what your heart rate was doing. An at-home stand test is a structured way to capture that same information the same way each time, so that ten of them can be compared to each other. It is not a diagnosis and it is not a tilt-table test, but it turns “I feel awful when I stand” into a set of numbers that arrive with dates attached.

This article is general information, not medical advice, and it cannot tell you what is happening in your body. Orsa is not a medical device and does not diagnose, treat, screen for or rule out any condition. If you faint, have chest pain or feel unwell, seek medical care.