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Complete lack of consciousness, with loss of reaction to stimulus and of spontaneous nervous activity. It is usually associated with cerebral injury of metabolic or physical origin. Simple concussions cause short losses of consciousness. Coma from lack of oxygen may last several weeks and is often fatal. Coma caused by stroke can be sudden, while that caused by metabolic abnormalities (as in diabetes mellitus) or cerebral tumours comes on gradually. Treatment depends on the cause.
This entry comes from Encyclopædia Britannica Concise. For the full entry on coma, visit Britannica.com.