A coma, or comatose is a deep state of unconsciousness - longer-term comatose patients may be reclassified as being in a permanent vegetative state. The patient cannot be awakened and does not respond to pain, light or sound in a normal way - the person in coma cannot react with the surrounding environment. A person in a coma does not take voluntary actions and does not have sleep-wake cycles. The inability to waken differentiates coma from sleep. Levels of unconsciousness and unresponsiveness vary, depending on how much of the brain is functioning... 
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