A coma is a profound state of unconsciousness. According to the contemporary medicine world, a  person in a coma cannot be awakened, fails to respond normally to pain, light or sound, does not have sleep-wake cycles, and does not take voluntary actions.

 

Coma may result from a variety of conditions, including intoxication, metabolic abnormalities, central nervous system diseases, acute neurologic injuries such as stroke, and hypoxia. A coma may also result from head trauma caused by mechanisms such as falls or vehicle collisions. The underlying cause of coma is bilateral damage to the reticular formation of the hindbrain (also known as the rhombencephalon), which is important in regulating sleep. Coma usually necessitates admission to a hospital and often the intensive care unit.