The Dancing Plague of 1518
In July 1518, a woman named Frau Troffea turned onto a narrow street in Strasbourg and began dancing. Not a waltz, a tango, or the dreaded Macarena, but a tortured, convulsed, involuntary dance fever that gripped her for days. It would be one thing if this was an isolated case of psychosis, but Troffea's creepy moves were somehow contagious, and about 400 people were infected with the so-called "dancing plague" over the next month. Many of them died of exhaustion, heart attacks, or strokes, and we HAVE NO IDEA WHY. The event is widely recorded, but other than chalking the whole thing up to "mass hysteria" — which is hardly a satisfactory explanation — the reason dozens of people boogied into their graves remains unknown.