Romeo lost in woods can't help losing it (7)
I believe the answer is:
corpses
'can't help losing it' is the definition.
(to corpse is to laugh during a performance)
'romeo lost in woods' is the wordplay.
'romeo' becomes 'r' (phonetic alphabet: alpha, bravo, charlie etc.).
'lost in' is an insertion indicator.
'woods' becomes 'copses' (a copse is a small wood).
'r' going within 'copses' is 'CORPSES'.
(Other definitions for corpses that I've seen before include "remains" , "Goofs on stage" , "Dead bodies" .)