A coma is a deep state of unconsciousness in which the individual is unresponsive to stimuli and produces no movement or speech. A person in a coma appears as if they are asleep. More than half of all comas are a result of brain injury or trauma. Other causes include the buildup of toxins, stroke, blood sugar level extremes (too low or too high), infection, or oxygen deprivation. Some comas are easily reversable while some are permanent.