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Barbara Myers and her guest Professor Richard Sutton from St Mary's Hospital in Paddington answer callers' questions about fainting.

Fainting is part of a wider syndrome known as syncope - a temporary loss of consciousness due to a lack of blood supply to the brain. Fainting is the most common cause of syncope.

Although it seems dramatic, fainting is not considered dangerous by doctors. 50% of us will faint at some point during our lives.

The second most common cause of syncope is caused by a sudden loss of blood pressure whilst standing - this is usually caused by the side effect of a prescribed medicine, or by a fairly rare condition known as postural hypotension.

The third, and most worrying cause of syncope might be due to an underlying heart condition, a form of cardiac rhythm disturbance which may either mean the heart stops momentarily, or beats very fast and inefficiently.

Another cause of sudden loss of consciousness is epilepsy, and if patients suffer from frequent fainting it's important for doctors to discover whether it's epilepsy or syncope which is causing it.