Coma

In medicine, a coma (from the Greek koma, meaning deep sleep) is a profound state of unconsciousness. A comatose patient cannot be awakened, fails to respond in general to pain or light, does not contain 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. It may also be intentionally induced by pharmaceutical agents in order to preserve higher brain function following another form of brain trauma.

Distinctive phases of coma
Within coma itself, there are some categories that describe the severity of impairment. Contrary to popular belief, a patient in a comatose state does not always lay still and quiet. They may talk, walk, and perform other functions that may occasionally appear to be conscious acts, yet are not.
Two scales of measurement regularly used in TBI diagnosis to determine the phase of coma are the Glasgow Coma Scale and the Ranchos Los Amigos Scale. The GCS is a simple 15-point scale used by medical professionals to assess severity of neurologic trauma, and establish a prognosis. The RLAS is a more complex scale that describes up to eight separate levels of coma, and is often used in the first few weeks or months of coma while the patient is under nearer observation, and when shifts between levels are more frequent.