Coma

Coma is a state of unconsciousness in which a person cannot be awakened, fails to respond normally to painful stimuli, light, or sound, lacks a normal wake-sleep cycle, and does not initiate voluntary actions. It usually develops gradually over a period of time, and can be caused by a variety of medical conditions, including trauma, stroke, drug overdose, or metabolic disorders. Its manifestations vary, from a deep state of unconsciousness to a persistent vegetative state.