Not working - case of reasonable pain (7)
I believe the answer is:
resting
'not working' is the definition.
(I've seen this before)
'case of reasonable pain' is the wordplay.
'case of' says to hollow out the word (remove centre letters) (outsides of).
'pain' becomes 'sting' (sting is a kind of pain**).
'reasonable' with its middle taken out is 're'.
're'+'sting'='RESTING'
(Other definitions for resting that I've seen before include "not in a cast" , "(Of actors) currently unemployed" , "Reposing" , "Relaxing from work" , "Taking a break" .)