Break bed's head, preferably clutching sweetheart (8)
I believe the answer is:
breather
'break' is the definition.
(I know that breather is a type of relief)
'bed's head preferably clutching sweetheart' is the wordplay.
'head' suggests taking the first letters.
'preferably' becomes 'rather' (synonyms).
'clutching' is an insertion indicator.
'sweetheart' becomes 'e' (the heart/centre of 'sweet').
The first letter of 'beds' is 'b'.
'rather' enclosing 'e' is 'reather'.
'b'+'reather'='BREATHER'
(Other definitions for breather that I've seen before include "A rest - lung?" , "quick break" , "lung or > liver?" , "state" , "Recovery time" .)