Fainting is a temporary loss of consciousness that happens when the brain does not receive enough oxygen. It comes on suddenly, only lasts for a short time and you recover fully within a short time. It is also often called a blackout. The medical term is syncope. It isn't the same thing as a seizure which usually causes jerking.
It is important to seek medical attention if you experience faints. Faints may be caused by a serious problem. However, this is unusual. The most common causes are mentioned below.
What happens when you faint?
When you faint, you become unconscious for a few seconds. It is also called passing out or blacking out. The medical term for this is syncope. You may feel sick and sweaty first or pass out with no warning signs at all.
When you pass out, you fall to the ground. It isn't the same thing as a seizure which usually makes you jerk. You come around after a few seconds and feel back to normal. Some people feel very tired after they've come around. Usually, fainting happens for a reason, like when you're in pain or have been standing for a long time in a hot place.
Fainting happens because the brain needs a constant supply of oxygen. If that supply falls below a certain level, we fall to the ground, which makes it easier for the more oxygen-rich blood to reach the brain.
What causes fainting?
Here are some of the more common causes of faints:
Common faint: this is also known as vasovagal syncope, neurologically mediated syncope (NMS) or a 'simple faint'. It is the most common cause of fainting. This can occur in various situations. These include:
- Severe pain or emotional distress.
- Witnessing something distressing; for example, some people faint at the sight of blood.
- After extreme exercise.
- After prolonged standing, especially in hot places (which is why soldiers on parade may faint).
- When wearing tight collars that constrict the neck.
During attacks, you may look pale and feel sweaty. Your eyes will usually stay open.
Orthostatic hypotension/postural hypotension. Normally, when we stand up, our blood pressure either stays the same or increases a bit. In orthostatic hypotension, people experience a sudden drop in blood pressure in standing up, which can cause them to faint. It can occur:
- Due to medication prescribed to lower blood pressure.
- During being sick (vomiting) or experiencing runny stools (diarrhoea) and other reasons for having a lack of fluid in the body (being dehydrated).
- As a result of neurological diseases such as Parkinson's disease and peripheral neuropathy.
- As a result of a rare hormonal condition called Addison's disease.
- After a big meal.
Cardiac syncope. This is any faint that's caused by a heart problem. Examples of heart problems include abnormal heart rhythms (arrhythmias) and narrowing of the heart valves. The faint may be preceded by chest pain or the sensation of having a 'thumping heart' (palpitations) and may happen during exercise. Some causes of cardiac syncope are inherited, and can cause sudden unexplained death; having a family history of sudden unexplained death may mean that you are at higher risk of developing cardiac syncope.
How common is fainting?
Fainting is common at all ages and affects up to 4 in 10 people at least once in their lives. Most people never get medical help. Most people (95%) have their first attack of syncope before they're 40 years old.
If you have it for the first time after 40, it is more likely to be due to a serious underlying problem. The most common cause is a common faint, also called neurally mediated syncope (NMS).
Common faints usually happen for the first time in teenage years and affect girls more than boys. In older people, fainting is more likely to be due to an underlying heart problem, low blood pressure or as a side-effect of medication.
Should I see a doctor if I faint?
You should call an ambulance if you have had a faint and:
- Have a blackout while exercising or lying down.
- Have a family history of sudden and unexplained deaths.
- Experience chest pain or the sensation of a 'thumping heart' (palpitations).
If the attack happens again or you do not feel completely back to normal, you should also seek urgent medical attention. In all other cases, you should see your GP. If you have lots of attacks, or you hurt yourself because of the faints, your GP may want you to see a specialist. They may also want you to see a specialist if your faints could affect your driving.
What investigations might be advised?
The doctor will want to know more about what you were doing when you blacked out. Understanding exactly what happened before, during, and after the faint is very important for diagnosing the cause.
- You will be asked whether you've recently started new medication.
- Try to remember whether you had any warning before you blacked out.
- Did anyone see you fall? (If so, ask them to speak to the doctor if possible).
- How did you feel when you came around?
These details will help the doctor to make a diagnosis. Your doctor will examine you. They will check your heart, including your blood pressure when sitting and standing and your pulse. You may be asked to have a heart tracing (an electrocardiogram, or ECG). You may have blood tests for anaemia and diabetes. Further tests of your heart and nervous system may be necessary.
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What else could it be?
Other causes of blacking out may be due to low blood sugar (hypoglycaemia) and lack of oxygen (hypoxia) from a variety of causes. It may be due to over-breathing (hyperventilation) but this is rare.
You may also black out after a fall or blow to the head or due to excess alcohol or street drugs.
Prolonged blackout, confusion after the event, incomplete recovery and tongue biting all suggest that the cause is not a simple faint.
Treatments for fainting and syncope
Treatment will depend on the likely cause of your blackout. You may be asked to keep a diary of your faints, including what you were doing when each happened. Most people can be seen and treated by their GP, but some may need to be referred for further investigation and treatment at a hospital.
How to prevent fainting
If you feel like you're going to faint, you can:
- Lie down flat with your legs up on a chair or against a wall or sit down on the ground with your head between your knees. Do not just sit on a chair.
- Squatting down on your heels can be very effective and is less noticeable in public.
- When feeling better, get up carefully. If symptoms return, resume the position.
If you faint again:
- Discuss with your doctor stopping any medication that may be responsible.
- Avoid alcohol.
- Drink more fluids such as water or soft drinks.
- Wear support stockings.
- Do leg crossing and arm tensing exercises.
You will need to find the underlying cause and try to address it if possible. Common faints are by far the most common cause. Many people who faint know when it tends to happen and how to avoid attacks.
Driving and faints
The Driver and Vehicle Licensing Agency (DVLA) rules on driving and faints depend on the exact cause of the faint, and the type of license held.
For Group 1 (car and motorcycle) license holders, 'simple' faints (vasovagal syncope) that occur only whilst standing do not need to be reported to the DVLA. However, group 2 (lorry, bus, and coach) license holders have stricter rules, and must stop driving and inform the DVLA.
The rules differ for other causes of faints. Speak to the DVLA and ask your doctor if in doubt.
What is the outlook?
Outlook (prognosis) depends on the underlying cause.
Many people get simple faints (vasovagal syncope) only once or twice. Identifying and avoiding triggers for a fainting spell can help to prevent them happening.
The outlook for other causes of faints depends on the cause. Some causes can be easily treated, whereas others can be challenging to fix.
Further reading and references
Transient loss of consciousness ('blackouts') management in adults and young people; NICE Clinical Guideline (August 2010 last updated November 2023)
Syncope (Guidelines on Diagnosis and Management of); European Society of Cardiology (ESC) Clinical Practice Guidelines (2018).
Kidd SK, Doughty C, Goldhaber SZ; Syncope (Fainting). Circulation. 2016 Apr 19133(16):e600-2. doi: 10.1161/CIRCULATIONAHA.115.017308.
Wieling W, Thijs RD, van Dijk N, et al; Symptoms and signs of syncope: a review of the link between physiology and clinical clues. Brain. 2009 Jul 8.