Why do I get dizzy when I stand up? The blood-pressure drop behind that head-rush

The head-rush that greys your vision for a second or two after you stand up is usually a brief drop in blood pressure. When you rise, gravity pulls roughly half a litre of blood down into the legs and abdomen, and if the circulation is slow to clamp down and push it back up, the pressure feeding the brain dips and you feel light-headed. When that dip is large enough and lasts, it has a name: orthostatic hypotension, defined by an international consensus as a sustained fall of at least 20 mmHg in systolic or 10 mmHg in diastolic blood pressure within three minutes of standing [s1].

It is one of the most common causes of dizziness, and for most people most of the time it is a plumbing problem — too little fluid on board, or a medication — rather than a sign of disease [s2].

What is actually happening

Standing is a small cardiovascular challenge that a healthy body meets automatically: sensors in the arteries detect the falling pressure and the autonomic nervous system tightens blood vessels and nudges up the heart rate to compensate, all within a few heartbeats. Orthostatic hypotension is what happens when that reflex is too weak, too slow, or overwhelmed.

The consensus separates the patterns by timing, which matters because they feel and behave differently [s1]. Classic orthostatic hypotension is the sustained 20/10 mmHg fall within three minutes described above [s1]. Initial orthostatic hypotension is a larger but very brief drop — at least 40 mmHg systolic and/or 20 mmHg diastolic within the first 15 seconds of standing — the transient swimmy feeling familiar to plenty of young, healthy people who jump up too fast, which then passes as the pressure recovers [s1]. A delayed fall, coming on only after three minutes, is the third pattern [s1]. The distinction is why a clinician measures blood pressure both immediately and after standing a while.

Common, and more so with age

Orthostatic hypotension is age-dependent, ranging from about 5% of people under 50 to around 30% of those over 70 [s2]. The gradient is steep, and it explains why the symptom is so much more of a fixture in later life.

The everyday triggers are the ones to think of first. Dehydration and anything that lowers blood volume make the fall bigger. So does medication: the review notes that orthostatic hypotension frequently complicates the treatment of high blood pressure, heart failure and coronary heart disease — that is, the drugs used to lower pressure can lower it too far on standing [s2]. Warmth, a heavy meal and alcohol all widen blood vessels and can tip a borderline system over. If you want to know where your resting pressure actually sits, our guide to home blood-pressure measurement and the piece on what counts as high cover the basics.

When the dizziness is a signal, not a nuisance

Two things lift orthostatic hypotension out of the nuisance category. The first is what it can point to: while it often occurs with no underlying disease, a persistent, symptomatic fall can be a marker of disease in the autonomic nervous system that regulates blood pressure, including neurodegenerative conditions [s2]. The second is what it can cause and predict. Beyond disabling symptoms, faints and traumatic injuries from falls, its presence independently increases mortality and the incidence of heart attack, stroke, heart failure and atrial fibrillation, even when it causes few symptoms [s2]. That association does not mean the dizziness itself is dangerous, but it does mean the finding is worth taking seriously rather than shrugging off.

For an older person, the fall risk is the immediate concern, and reducing hazards in the home is one of the few things with trial support behind it, covered in our report on falls prevention. Recurrent fainting that is not clearly a simple head-rush is investigated differently again — sometimes with prolonged heart-rhythm monitoring, as in our piece on unexplained syncope.

What it means for a reader

An occasional, brief head-rush on standing quickly, especially when you are hot, tired or under-watered, is common and usually benign [s1]. Dizziness that is frequent, that comes with actual faints or falls, that arrives after starting or changing a blood-pressure medication, or that travels with neurological symptoms, is the kind that a clinician should measure and work up [s2]. This article is informational and is not medical advice; it does not recommend starting, stopping or changing any medication.

Sources

• Consensus statement on the definition of orthostatic hypotension, neurally mediated syncope and the postural tachycardia syndrome — Clinical Autonomic Research, 2011-03-24
• Orthostatic Hypotension: Epidemiology, Prognosis, and Treatment — Journal of the American College of Cardiology, 2015-08-10