A coma is a deep state of unconsciousness. It can occur as a complication of an illness, exposure to a drug, alcohol, or toxin, or as a result of injuries, such as head trauma. A coma is a medical emergency.
People in a coma generally recover but some don't. It can be very difficult to predict recovery when a person is in a coma. Sometimes a coma is followed by a persistent vegetative state.
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Last reviewed: July 2016