syncope

n. A brief lapse in consciousness (commonly called fainting). The cause is a transient loss of cerebral oxygenation, which may result from a variety of external and/or internal events. These events may include stimulation of the vagus nerve, which affects parasympathetic control, slowing the heart rate and decreasing the availability of oxygen to the brain. Also, a parasympathetic rebound from sympathetic activity in the abdominal viscera (a vaso-vagal phenomenon) may produce syncope. Extreme temperature, emotional stress, or hypoglycemia may also induce syncope. Syncope may be prevented or minimized by lying down flat or by sitting with the head between the knees. It is possible that the acupressure point for fainting, pressure applied between the upper lip and nostrils, may also prevent or minimize syncope. The use of an ammonia inhalant capsule may revive a person who is fainting or has just fainted. – VS