What causes coma?

A coma may be caused by many different things, but ultimately a coma occurs when the part of the brain, called the reticular activating system, which controls arousal, and the cerebrum on the upper part of the brain, is not functioning properly. Traffic accidents and violence cause comas more than any other illness or injury. Many illnesses may cause the reticular activating system or the cerebrum to malfunction, including tumor, aneurysm, seizures, stroke, lack of oxygen, or diabetes. Taking too many medications, illegal drugs, or alcohol can also result in a comatose state.