Resting as skin comes back (6)
I believe the answer is:
asleep
'resting' is the definition.
(I've seen this before)
'as skin comes back' is the wordplay.
'skin' becomes 'peel' (synonyms).
'comes back' says the letters should be written backwards.
'peel' backwards is 'leep'.
'as'+'leep'='ASLEEP'
(Other definitions for asleep that I've seen before include "Like kippers" , "Dozing" , "Napping" , "Snoozing" , "In the arms of Hypnos" .)