After visiting the theatre one may be laughing uncontrollably (2,8)
I believe the answer is:
in stitches
I believe this clue is a double definition.
'after visiting the theatre one may be' is the first definition.
(after visiting an operating theatre)
'laughing uncontrollably' is the second definition.
(I've seen this before)
(Other definitions for in stitches that I've seen before include "Laughing a lot" , "as one may be on leaving the theatre?" , "much affected by comedy?" , "extremely amused" , "Helpless with laughter" .)