Deep unconsciousness (4)
I believe the answer is:
coma
'deep unconsciousness' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for coma that I've seen before include "State of deep (often prolonged) unconsciousness" , "State of insensibility" , "Unconscious state" , "State of unconsciousness caused by illness" , "long sleep" .)