Fainting (syncope): causes, red flags and when to see a doctor

Fainting is when you pass out for a short time. The NHS says it usually happens suddenly, though many people notice warning signs first: dizziness, sweating, a feeling of warmth or heat, feeling sick and changes in vision. Blood pressure or blood flow to the brain drops briefly, consciousness is lost, and the person falls, which restores blood flow and brings them round.

Doctors use the word syncope for transient loss of consciousness caused by reduced blood flow to the brain, as distinct from seizures, low blood sugar or head injury, which can look similar to onlookers. The NHS includes a seizure among the reasons to call 999 and low blood sugar among symptoms that can cause confusion.

The NHS lists the causes of fainting as standing up too quickly, which can 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, and taking drugs or drinking too much alcohol.

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 heart palpitations (a pounding, fluttering or irregular heartbeat), has seriously hurt themselves before or after fainting, is shaking or jerking as in a seizure, fainted while exercising or fainted while lying down. It says not to drive yourself to A&E and that the 999 operator will give advice.

For atrial fibrillation the NHS says to call 999 if a fast or irregular heartbeat comes with fainting, feeling dizzy or falling over, chest pain, shortness of breath, sweating, feeling sick, a severe headache, weakness or numbness on one side, blurred vision or loss of sight, or confusion or difficulty speaking. NICE CKS for palpitations lists exercise-triggered palpitations, palpitations with associated symptoms such as fainting, and a family history of sudden cardiac death under 40 as reasons for urgent cardiology referral.

Even without these features, the NHS says anyone who has fainted should see a GP.

• Fainting during exercise or while lying down.

• Chest pain, palpitations or an irregular heartbeat around the time of the faint.

• Not breathing, or not waking within a minute.

• Shaking or jerking movements, or a slow recovery with confusion.

• Serious injury from the fall.

• A family history of sudden cardiac death or unexplained early death.

The doctor will ask for a description from you and from any witness: what you were doing, what you felt beforehand, how long you were out, whether you shook, how quickly you recovered, and previous faints. They will ask about medicines, alcohol, drugs, fluids, meals, heart or neurological conditions and family history. CKS for palpitations lists personal or family history of heart disease, arrhythmia or sudden cardiac death under 40 among the key questions, and these apply equally to fainting.

Examination includes pulse, blood pressure sitting and standing, heart sounds, and a neurological check. The NHS low blood pressure page says blood pressure can be checked by a pharmacist, practice nurse or GP, or at home with a monitor.

A resting ECG is the key first test, as it can reveal rhythm and conduction problems. CKS describes a 12-lead ECG, ideally during symptoms, and the NHS atrial fibrillation page lists an ECG, echocardiogram, chest X-ray and blood tests. Heart rhythm monitors worn for a day or longer are used when symptoms are occasional. Lying and standing blood pressure checks identify postural hypotension.

Depending on the history, blood tests for anaemia, blood sugar, salts and thyroid, tilt-table testing for suspected vasovagal or postural causes, and referral to cardiology or neurology may follow.

The NHS says if you feel as if you are about to faint, lie down with your legs raised or sit with your head lowered between your knees, drink some water, cross your legs while standing or rock up and down on your toes, and clench your fists. The NHS low blood pressure page adds getting up slowly from sitting or lying and eating small, frequent meals.

If you see someone faint, the NHS says check whether they respond by gently shaking their shoulders and asking loudly if they are OK. If not, shout for help, tilt their head back and lift the chin, and listen for at least 10 seconds for breathing. If they are breathing normally, lay them on their back and raise their legs; a pregnant person, especially beyond 28 weeks, should be laid on their side.

The NHS says anyone who has fainted should see a GP. The GP may refer to cardiology or a specialist syncope or falls service. A pharmacist or practice nurse can check blood pressure.

On driving, the NHS says you must tell the DVLA if you are fainting regularly because it could affect your ability to drive, and you must not drive if you have been referred to a specialist and are waiting to be assessed.