It was centuries ago, right around this time, when the city of Aachen, Germany, was struck by an unusual outbreak that, legend says, spread as far away as Madagascar.

According to the scant written accounts there are of the outbreak known as St. Vitus’ Dance, back in 1374, groups of people — sometimes thousands at a time — started dancing uncontrollably. It continued for days, and in some cases, weeks and months. Some people reportedly danced until they collapsed from exhaustion or even death, while others suffered heart attacks and broken bones.

“One written account described people as united by one common delusion,” said James Fowler, professor of medical genetics and political science at the University of California, San Diego.

The dancers also seemed to hallucinate and lose control of their senses, Fowler said.

Continue Reading on