This is kind of random, but I just heard about this bizarre historical event from a good friend of mine. And I figure, most vintage folks like history beyond just the era they dress in, right? Right? Okay.
So, I won't bother giving a full history of the event, when these articles, from the Discovery Channel and Wikipedia, do it so much better, but here's the general idea: in the summer of 1518, one woman in Strasbourg, France stopped in the streets and began to dance intensely, in a trance - and didn't stop for four to six days! Other people, seemingly overtaken by the same trance, joined her, and within the week 34 others had joined, and in a month, 400 had joined in! Many actually died from the dancing - heart attack, exhaustion, and strokes. At the time doctors proclaimed it was a natural disease caused by "hot blood".
The Discovery Channel article also cites examples of another dancing plague in Madagascar in the 1840s, and the Laughter Epidemic of 1962 (which lasted eighteen months!!).