Fainting: causes, symptoms, what to do and when to see a doctor

The NHS says there are many reasons why someone might faint. Fainting happens when the brain briefly does not get enough blood and oxygen. The NHS lists these causes.

• Standing up too quickly, which could be a sign of low blood pressure.

• Not eating or drinking enough.

• Being too hot.

• Being very upset, angry or in severe pain.

• Heart problems.

• Taking drugs or drinking too much alcohol.

NICE guideline CG109 on transient loss of consciousness describes how clinicians recognise the commonest types.

An uncomplicated faint (vasovagal syncope) is diagnosed when there are no features suggesting another cause and the "3 Ps" are present: posture (prolonged standing, or similar episodes prevented by lying down), provoking factors (such as pain or a medical procedure) and prodromal symptoms (such as sweating or feeling warm or hot before losing consciousness). NICE notes that brief seizure activity can occur during uncomplicated faints and is not necessarily epilepsy.

Situational syncope is diagnosed when fainting is clearly and consistently provoked by straining while passing urine (usually standing) or by coughing or swallowing. Postural hypotension is suspected when symptoms are typical and lying and standing blood pressure confirm a drop.

The NHS says fainting usually happens suddenly. Symptoms before the faint can include the following. NICE says clinicians ask about the circumstances, posture beforehand, prodromal symptoms, how the person looked, any limb-jerking, tongue-biting, injury, how long it lasted and any confusion afterwards.

• Dizziness.

• Sweating.

• Feeling warm or hot.

• Feeling sick.

• Changes to your vision.

The NHS says that usually the person who has fainted will wake up within 30 seconds. If they cannot be woken within 1 minute, it is an emergency: call 999. The NHS advises seeing a GP after you have fainted, to find out what may have caused it.

The NHS gives these steps if you are with someone who has fainted.

• Stay calm. Check whether they respond by gently shaking their shoulders and asking loudly if they are OK.

• If they do not respond, shout for help and gently tilt back their head and lift their chin to help them breathe more easily.

• Check for normal breathing by listening for at least 10 seconds.

• If they are breathing normally, lay them on their back and raise their legs. If they are pregnant, especially more than 28 weeks, lay them on their side instead.

• If you feel you are about to faint yourself: lie down with your legs raised, or sit with your head lowered between your knees; drink some water; cross your legs while standing and rock up and down on your toes; clench your fists.

The NHS says you may feel faint while pregnant. Fainting happens if your brain is not getting enough blood and therefore not enough oxygen. You are most likely to feel faint if you stand up too quickly from a chair or out of a bath, but it can also happen when you are lying on your back.

The NHS suggests getting up slowly after sitting or lying down; if you feel faint when standing still, finding a seat quickly (and lying down on your side if it does not pass); and if you feel faint lying on your back, turning onto your side. It is better not to lie flat on your back in later pregnancy or during labour, and the NHS says you should avoid going to sleep on your back after 28 weeks, as it has been linked to a higher risk of stillbirth.

Mention fainting to your midwife, and contact your maternity unit or NHS 111 sooner if it keeps happening or you are hurt. The sources used here give the general NHS advice only, and your maternity team can look for the cause.

The NHS says to call 999 if someone is not breathing, cannot be woken within 1 minute, has not fully recovered or has difficulty with speech or movement, has chest pain or a pounding, fluttering or irregular heartbeat, has seriously hurt themselves before or after fainting, is shaking or jerking, fainted while exercising, or fainted while lying down. Do not drive yourself to A&E.

NICE says that someone who faints and has an abnormal ECG, heart failure, faints during exertion, has a family history of sudden cardiac death under age 40 or an inherited heart condition, new or unexplained breathlessness or a heart murmur should be referred urgently for cardiovascular assessment, prioritised by a specialist within 24 hours. NICE also suggests considering urgent assessment for anyone over 65 who faints without warning symptoms.

Yes. The NHS says it is probably nothing serious but it is important to get checked by a GP to find out what might have caused it. A GP will usually ask what happened before, during and after the faint, ask about medical history, family history of heart disease and medicines, check pulse and blood pressure lying and standing and record an ECG, as NICE recommends. Most people with a clear uncomplicated faint need no further tests.

The NHS low blood pressure page also advises getting your blood pressure checked if you keep getting symptoms such as lightheadedness, dizziness, blurred vision, weakness, confusion or fainting. Low blood pressure is a reading of less than 90/60mmHg.

The NHS says you must tell the Driver and Vehicle Licensing Agency (DVLA) if you are fainting regularly, as it could affect your ability to drive. You must not drive if your GP has referred you to a specialist and you are waiting to be assessed. GOV.UK has details on how to tell the DVLA about fainting or blackouts.

It can be hard to tell a faint from a seizure. NICE advises a specialist epilepsy assessment within 2 weeks for people with features strongly suggestive of epilepsy, shown in the table. Brief shaking can occur during an ordinary faint.

On the NHS, a GP is the first step after a faint, with 999 for emergencies. Referral to a cardiology, falls or syncope service follows if there are red flags or the cause is unclear. Specialist clinics can arrange further heart tests where needed.

Private cardiology and syncope clinics offer ECGs, monitoring and specialist review, usually with shorter waits. The same red-flag rules apply in either setting; do not delay emergency care for a faint with chest pain, palpitations or exertion.