I always enjoy these side diversions, because they're full of "Huh, WTFs". In English I'd never heard anyone call it anything but "a stitch"¹ colloquially or ETAP as an actual condition, but sure enough side ache features in the list of alternatives on Wikipedia.

Oddly, Wiktionary has an article for sideache² and a link to that page if you look for side stitch. Makes me curious how often that is the case now. [/me sniped]

¹ https://en.wikipedia.org/wiki/Side_stitch

² https://en.wiktionary.org/wiki/sideache