A COMA is a state of unconsciousness caused by severe injury or illness, lasting for an extended period of time. A TRANCE is a state of altered consciousness in which a person appears to be asleep or in a dream-like state. Finally, a STUPOR is a state of near-unconsciousness, characterized by a lack of response to external stimuli. All three of these states of unconsciousness are characterized by a lack of awareness and responsiveness to the environment.