Fainting (syncope) is a sudden temporary loss of consciousness that usually results in a fall.
When you faint, you'll feel weak and unsteady before passing out for a short period of time, usually only a few seconds.
There may not be any warning symptoms, but some people experience:
Read more about the symptoms of fainting.
If you feel you're about to faint, lie down, preferably in a position where your head is low and your legs are raised. This will encourage blood flow to your brain.
If it's not possible to lie down, sit with your head between your knees. If you think someone is about to faint, you should help them lie down or sit with their head between their knees.
If a person faints and doesn't regain consciousness within one or two minutes, put them into the recovery position.
You should then dial 999, ask for an ambulance and stay with the person until medical help arrives.
Most cases of fainting aren't a cause for concern and don't require treatment, but less common types of fainting can be medical emergencies.
You should see your GP after fainting if you:
If your first episode of fainting occurs after 40, it may be a sign of a more serious underlying problem.
Read more about diagnosing fainting.
The brain relies on oxygen carried in the blood to function properly. Fainting can occur when the blood flow to the brain is reduced.
Your body usually corrects reduced blood flow to the brain quickly, but it can make you feel odd, sweaty and dizzy. If it lasts long enough, you may faint.
Reduced blood flow to the brain is often caused by a temporary problem with the part of your nervous system that regulates the body's automatic functions, including heartbeat and blood pressure.
This type of fainting is called neurally mediated syncope. It can be triggered by:
Read more about the causes of fainting.
Treatment for fainting will depend on the type you're experiencing. In many cases of neurally mediated syncope, no further treatment is needed.
If you've had a fainting episode, you can avoid it happening again by:
Read more about how fainting is treated.