Vasovagal syncope

How it works

The vagus nerve is the main brake on the heart. It also controls the width of many blood vessels³. In a vasovagal faint, this brake is pulled far too hard. The heart slows, sometimes to a near stop for a few seconds. At the same time the blood vessels in the legs and gut relax and widen. Blood pressure falls. Not enough blood reaches the brain, and the brain switches off for a moment¹.

Falling over is the cure. Once you are flat, blood no longer has to climb against gravity. The brain refills and you wake within seconds to a minute. Most people feel washed out and sweaty afterwards¹.

Common triggers are the sight of blood or needles, sharp pain, fear, heat, standing still for a long time, dehydration, coughing, and straining on the toilet¹. A faint usually gives warning. People feel light-headed, their vision narrows or goes grey, sounds fade, they feel sick, and they turn pale and sweaty². Sitting or lying down at the first sign often stops the faint.

Roughly 4 in 10 people faint at least once in their life, and this reflex is the most common cause¹. It is more common in teenagers and young adults².

Is it a problem?

By itself, no. The reflex does not damage the heart or the brain. The main risk is the fall. If you feel a faint coming, lie down and raise your legs, or sit with your head between your knees.

See a doctor if any of these apply²:

• You fainted during exercise, or while lying down.
• There was no warning at all.
• You had chest pain, a racing heart, or a pounding heartbeat before the faint.
• You were unconscious for more than a minute, or your body jerked for a long time.
• Someone in your family died suddenly at a young age from a heart problem.
• You faint often, or the first faint happened after the age of 60².
• You were injured in the fall.

Call emergency services if someone faints and does not wake within a minute, or has trouble breathing.