Dancing Plague of 1518
Okay, this is just weird.
The Dancing Plague (or Dance Epidemic) of 1518 was a case of dancing mania that occurred in Strasbourg, France (then part of the Holy Roman Empire) in July 1518. Numerous people took to dancing for days without rest, and, over the period of about one month, most of the people died from heart attack, stroke, or exhaustion. (via lamusiqueestlavie)