Not asleep (5)
I believe the answer is:
awake
'not asleep' is the definition.
('awake' is the opposite to 'asleep')
This is all the clue.
(Other definitions for awake that I've seen before include "Conscious, aware" , "Patriotic song 'The West's .....'" , "Tossing and turning" , "Unable to sleep" , "Cease sleeping" .)