definition of a coma
Coma By Mayo Clinic Staff. A coma is a state of prolonged unconsciousness that can be caused by a variety of problems â traumatic head injury, stroke, brain tumor, drug or alcohol intoxication, or even an underlying illness, such as diabetes or an infection. A 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.