A person who faints has a brief loss of consciousness, followed by immediate recovery. Those who faint are unable to maintain posture: they fall to the floor or slump in a chair when they lose consciousness, and then they become alert again quickly.

Fainting is caused by a sudden reduction in blood flow to the entire brain. The brain stops working when blood flow stops for more than a few seconds. About 60 percent of teenagers have an episode of fainting before they are 18 years old.