Rolling with laughter, as you may be after theatre trip (2,8)
I believe the answer is:
in stitches
If this is the answer I cannot explain how the clue works.
Can you help me to learn more?
(Other definitions for in stitches that I've seen before include "Helpless with laughter" , "Laughing a lot" , "as one may be on leaving the theatre?" , "much affected by comedy?" , "you may be laughing" .)