Complex sentence: Sufferers may vomit or retch six to twelve times an hour, and an episode may last from a few hours to well over 3 weeks, with a median episode duration of 41 hours (Li & Fleisher 1999).
Split into simpler sentences: Sufferers may vomit or retch six to twelve times an hour and an episode may last from a few hours to well over 3 weeks. The median duration of an episode is 41 hours (Li & Fleisher 1999).