There are various things that can interrupt the flow of blood to the brain and cause fainting:

• An external trigger that causes a temporary glitch in the autonomic nervous system, for example coughing, sneezing, pain, or seeing something unpleasant. This is known as vasovagal syncope
• A sudden drop in blood pressure, during which the blood vessels don’t constrict as they should do in order to force blood to the brain. This can happen when moving from lying or sitting to standing and is known as orthostatic or postural hypotension. It may be due to age, as the blood vessels become less elastic over time; medication; neurological conditions; or dehydration, which can stem from diabetes
• Heart problems, for example an issue arising with the structure of the heart itself, an abnormal heartbeat, or reduced blood supply to the heart meaning it doesn’t pump as efficiently as usual. This is known as cardiac syncope
• Involuntary slowing of the heart rate to the point that it stops beating for a few seconds. This is known as a reflex anoxic seizure and mainly occurs in young children, becoming less frequent as they grow and usually vanishing by the age of four or five years.

In the short-term, the best way to manage fainting it to get the patient’s head lower than their legs – if they are sitting, this can be achieved by encouraging them to sit with their head between their knees, otherwise if they are lying down their legs can be propped up on someone’s shoulder if they crouch down or an object such as a chair – and making sure they have plenty of air. Once they regain consciousness, they should continue to lie down until they are feeling steadier and then sit and stand gradually, perhaps sipping some water to counteract any contributing dehydration.