Fainting is a sudden loss of consciousness, usually cause by lack of oxygen in the brain. The medical term for fainting is syncope.
A fainting episode may or may not be due to medical illness. A person may faint at the sight of blood or due to hunger or dehydration. This is the commonest cause due to vasovagal. However, every episode of fainting should be given serious attention until the cause is known and symptoms treated. Certain heart conditions like hypertrophic cardiomyopathy and aortic stenosis can result in syncope and it is important to rule out any serious conditions of the heart as the underlying condition.