2018-12-22:
Dancing plague

In 1518, a woman began dancing in the streets of Strasbourg, and simply didn't stop. Within a month, around 400 dancers joined her. Some of them would later die of exhaustion, heart attacks, or strokes.

Modern explanations of this behavior center around a toxic wheat fungus, containing psychoactive substances similar to LSD. Several other dancing plague cases have been reported during the medieval era.