in stitches
Laughing uncontrollably, as in Joke after joke had me in stitches. Although the precise idiom dates only from about 1930, Shakespeare had a similar expression in Twelfth Night (3:2): "If you desire the spleen, and will laugh yourselves into stitches, follow me." Stitches here refers to the sharp local pain (known as a stitch in the side) that can make one double over, much as a fit of laughter can.