Stopped working, on getting drowsy (7)
I believe the answer is:
retired
'stopped working' is the definition.
(I've seen this before)
'on getting drowsy' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to'**).
'getting' says to put letters next to each other.
'drowsy' becomes 'tired' (I've seen this before).
're'+'tired'='RETIRED'
(Other definitions for retired that I've seen before include "Stopped work - went to bed" , "Finished work" , "Gave up job, relaxed on pension" , "No longer working" , "In bed, withdrew" .)