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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 but it is common to get "jerky" movements even in a simple faint, especially if sitting or slumped with the head up. 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, and so we regain consciousness.

Here are some of the more common causes of faints:

Vasovagal syncope (common 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:

• Miedo.

• Severe pain or emotional stress.

• 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.

Signs you're about to faint

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 (vómitos) or experiencing runny stools (diarrea) and other reasons for having a lack of fluid in the body (being dehydrated).

• As a result of neurological diseases such as enfermedad de Parkinson y neuropatía periférica.

• As a result of a rare hormonal condition called Enfermedad de Addison.

• After a big meal.

Cardiac syncope

This is any faint that's caused by a heart problem. Examples of heart problems include ritmos cardíacos anormales (arritmias) y narrowing of the heart valves. The faint may be preceded by dolor en el pecho o 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.

Other causes of syncope related to the heart include postural orthostatic tachycardia syndrome and syncope may also be causes by excessive sensitivity of the carotid artery (carotid sinus syncope), when factors such as shaving, head turning, neck extension or tight collars may cause 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, baja presión arterial or as a side-effect of medication.

• Advise them to lie down. Lie them down on their back, unless they are pregnant, when it's better to lie them on their side.

• If possible, elevate their legs slightly using a stool, cushions or pillows. Make sure they get plenty of fresh air and ask other people to stand back.

• Usually the person will regain consciousness within 30 seconds. Reassure them and help them to sit up slowly over a few minutes, when they feel better.

• Request an emergency ambulance (999 in the UK) if the person:

  • Is not breathing.

  • Cannot be woken up after 1 minute.

  • Have chest pain or heart palpitations.

  • Has suffered any serious injuries.

  • Has not fully recovered, especially if they have any difficulty with speech or movement.

  • Is having a fit with shaking or jerking.

  • Fainted while exercising or when lying down.

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Should I see a doctor if I faint?sain 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.

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 anemia y diabetes. Further tests of your heart and nervous system may be necessary.

The most common cause of blacking out is fainting. Other causes include epileptic seizures, syncope due to ansiedad (psychogenic pseudosyncope) and other rare causes of faints.

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.

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.

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.

• Evitar el 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.

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.

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.