Seeing stars when standing up

How it works

Standing up moves about 700 mL of blood from the chest into the legs, pulled by gravity¹. Less blood returns to the heart. For a moment, blood pressure at the head drops. Pressure sensors in the neck arteries detect the drop and tell the heart to beat faster and the blood vessels to tighten. This is the baroreflex². It takes a few seconds to catch up.

If the reflex is slow, the brain and the retina get slightly less blood for those seconds. The eyes and brain are sensitive to this. You may see spots, sparkles, grey, or a closing tunnel of vision. These are phosphenes caused by reduced blood flow³. The ears may ring and the legs may feel weak. It usually passes within a few seconds to half a minute¹.

It is worse when you are dehydrated, after alcohol, or when you have been lying down for a long time¹. It is common in healthy teenagers⁵.

How common it is

A brief, mild drop on standing is common and can happen to anyone¹. No study counts how many people have felt it. The clinical definition is a drop of at least 20 mmHg in systolic or at least 10 mmHg in diastolic blood pressure within three minutes of standing¹. That drop is measured in the lab with a blood pressure cuff, so it is a firmer figure¹. It affects about 5% of people under 50 and about 30% of people over 70⁴.

Is it a problem?

No, when it is brief. Sit or lie down and it passes. To prevent it, stand up slowly, drink enough water, and tense your leg muscles before you rise.

See a doctor if:

• you actually faint,
• it happens most times you stand,
• it comes with chest pain,
• your heart races for minutes rather than seconds,
• it happens during exercise rather than after it.

If you fall and hit your head, get checked.