Again exhausted, went to bed (7)
I believe the answer is:
retired
'went to bed' is the definition.
('retire' can be a synonym of 'go to bed')
'again exhausted' is the wordplay.
'again' becomes 're' (prefix meaning 'again').
'exhausted' becomes 'tired' (exhausted can mean very tired).
're'+'tired'='RETIRED'
(Other definitions for retired that I've seen before include "Finished work" , "went back" , "Gone to bed" , "Turned in" , "Stopped work - went to bed" .)