Cataplexy is a condition that involves a sudden, temporary loss of muscle tone. It is often caused by extreme emotional states, especially laughter, anger, and excitement. Cataplectic attacks vary in strength and duration. Mild attacks can consist of weakening of the knees or a drop of the jaw or head. Severe attacks can cause sudden paralysis of almost all muscles of the body, causing the person to collapse. A cataplectic attack may last from a few seconds to 20 minutes. The person remains conscious but cannot move the affected muscles. Cataplexy is often accompanied by narcolepsy, an irresistible urge to sleep 

Cataplexy is not a form of epilepsy. It is sometimes confused with catalepsy, the temporary loss of voluntary movement..