What should you know about causes of sudden fainting?

Fainting, also called syncope, happens when the brain briefly receives too little blood flow. Standing for a long time, heat, pain, fear, straining, or a sudden drop in blood pressure can trigger it. Fluid loss from vomiting, diarrhoea, fever, or not drinking enough may cause dehydration and make fainting more likely. Low blood sugar can occur when someone with diabetes misses food or uses more glucose-lowering medicine than needed. Anaemia reduces the blood’s oxygen-carrying capacity. Atrial fibrillation and other heart rhythm disturbances can reduce effective circulation or cause a rapid, irregular heartbeat.

The details around the event matter: warning symptoms, posture, activity, palpitations, injury, recovery time, and any witness account help clinicians assess the cause.

If someone feels faint, help them lie flat and raise their legs if there is no injury or breathing problem. Loosen tight clothing, provide fresh air, and do not give food or drink until they are fully alert. After recovery, rise slowly, drink fluids if appropriate, and arrange a medical assessment, particularly after a first episode. Bring a list of medicines and note what happened immediately beforehand.

Call emergency services if the person does not wake promptly, is not breathing normally, has chest pain, severe breathlessness, a new neurological problem, a serious injury, or a seizure. Urgent assessment is also needed when fainting occurs during exercise, while lying down, or with a racing or irregular heartbeat. Repeated episodes, pregnancy, known heart disease, or a family history of sudden cardiac death warrant prompt medical review.

Ask whether blood pressure checks lying and standing, an electrocardiogram, blood tests, or heart monitoring are suitable. Tell the clinician about fluid intake, meals, bleeding, new medicines, palpitations, and the exact sequence of symptoms before and after the event.