What is unconsciousness?

A person who is unconscious is not aware of what is going on around him or her. He or she may not be able to make purposeful movements.

A person may become unconscious from an injury or a health condition.

• Fainting or a seizure disorder (epilepsy) may cause unconsciousness that is usually brief.
• Heart problems, such as stroke, heart attack, or changes in heart rate or rhythm (arrhythmia), can block blood and oxygen to the brain and cause unconsciousness.
• Lack of adequate oxygen, such as when there is too much carbon monoxide in the air a person breathes, can cause a gradual unconsciousness.
• Head injuries can "knock out" a person, making him or her unconscious.
• Any event that leads to being in a coma, which is a deep, prolonged state of unconsciousness. Diabetic coma, caused by very high or very low blood sugar, is one type of coma.
• Heavy alcohol or drug use or problems caused by quitting their use (withdrawal) can cause the body to go into a state of shock that may cause unconsciousness. Heatstroke, an injury, or a traumatic event can also cause shock and unconsciousness.