Fainting is a temporary loss of consciousness caused by lack of oxygen in the higher parts of the brain. It is commonly the result of a fall in blood pressure and is more likely to occur when a person is standing. Fainting may be associated with real or imagined injuries, involving preparation of the body for fleeing. The enlargement of the blood vessels in the limbs lowers the blood pressure. The person becomes weak and nauseated and faints unless he sits or lies down. Loss of blood also causes fainting, as it reduces the blood pressure.
If you feel that you are about to faint, you should lie down. If this cannot be done, sit down and place the head between the knees, or kneel on one knee and place the head below the heart. Treatment of fainting includes loosening tight clothing, applying ammonia or smelling salts to the nose, and sprinkling the face with cold water. A person who has fainted should be kept lying down until completely recovered.