In stitches (4)
'in stitches' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sewn that I've seen before include "Fastened with thread" , "Fastened with needlework" , "What's embroidered" , "done with a needle" , "Run up" .)
(Other definitions for laughing that I've seen before include "Expressing loud amusement" , "Expressing mirth" , "Kookaburra" , "Showing mirth" , "Reacting to comedy" .)