Head Injury Coma
Coma is a state of brain function. A comatose patient cannot be awakened, fails to respond normally to pain or light, does not have sleep-wake cycles, and does not take voluntary actions. Coma in head injured people almost always results from injury to all parts of the brain. This may result in prolonged coma with rapid and nearly complete recovery when the head injured person wakes up.
The human brain performs at different levels of consciousness. The different levels of consciousness do not have distinct boundaries, but rather, the levels blend into each other. At the uppermost level the brain is perceived as alert, sharp, quick to respond to varying stimuli. At the lowermost level, the brain is in a state of coma. This state most frequently occurs abruptly rather than in phases, usually followed by a progressive recovery.