Coma is a state of prolonged unconsciousness that can be caused by a variety of problems — traumatic head injury, stroke, brain tumor, drug or alcohol intoxication, or even an underlying illness, such as diabetes or an infection.
Coma is a medical emergency. Swift action is needed to preserve life and brain function. Doctors normally order a battery of blood tests and a brain CT scan to try to determine what's causing the coma so that proper treatment can begin.
Comas seldom last longer than several weeks. People who are unconscious for a longer period of time may transition to a persistent vegetative state. Depending on the cause of coma, people who are in a persistent vegetative state for more than one year are extremely unlikely to awaken.