Quick answer
What could fainting mean?
Fainting (syncope) is a brief loss of consciousness caused by a temporary drop in blood flow to the brain. Most faints are vasovagal and people recover quickly after lying flat. See a GP after an unexplained faint or repeated episodes, and collapse during exercise always needs medical assessment.
What is fainting (syncope)?
Fainting — known medically as syncope — is a brief loss of consciousness caused by a temporary drop in blood flow to the brain. Most faints are harmless and people recover quickly, especially once they are lying flat. A small number of faints, however, have a cardiac cause and need proper assessment.
Causes of fainting
The most common cause is a vasovagal faint, a reflex reaction that can be triggered by pain, heat, strong emotion or standing still for long periods. Dehydration also contributes to fainting, and some medicines can lower blood pressure enough to cause a faint.
Less commonly, fainting is caused by a heart rhythm problem (arrhythmia), and these faints can be dangerous. Structural heart disease is a rare but serious cause that also needs specialist assessment.
How to prevent fainting
Drinking enough fluids and rising slowly from sitting or lying down both help to prevent faints. It is also worth learning to recognise your warning symptoms (the prodrome) so you can sit or lie down before you black out, and treating or avoiding your triggers where possible.
If you faint during pregnancy, tell your midwife.
When to see a GP about fainting
See a GP after a first unexplained faint, or if fainting keeps happening. Fainting during exercise (exertional syncope) always needs assessment, and people who collapse on exertion are usually referred to a cardiologist.
Common questions about fainting
- What first aid should I give someone who has fainted?
- Lay them flat on their back and raise their legs to help blood return to the brain. Make sure their airway is clear, and call 999 if they do not recover quickly.
- What triggers a vasovagal faint?
- Common triggers include pain, heat, strong emotion and standing still for long periods. Recognising your own triggers, and avoiding them where possible, can help prevent further faints.
- How do I know if fainting is heart-related?
- Fainting during exercise, or fainting alongside palpitations, raises the possibility of a heart cause. These episodes need medical assessment, usually starting with an ECG (a heart tracing).
- Can low blood pressure cause fainting?
- Yes, low blood pressure is a common reason for fainting. Dehydration and some medicines can both lower blood pressure enough to cause a faint, so ask your GP to review them.