Dancing plague or dancing mania was a medieval phenomenon and mystery. Throughout the period of middle ages, outbreaks of uncontrollable dancing mania would occur.
The mania affected thousands of people at the very same time: men, women, and children, all danced until they collapsed or died from exhaustion. The outbreaks usually occurred around the time of the feast of St Vitus. Because of the timing, the uncontrollable dance was called St. Vitus' Dance.
One of the biggest outbreaks occurred in 1518, in Strasbourg. A woman named Frau Troffea began dancing in the street. Within four days 33 people joined and within a month there were many as 400 infected with the bizarre disease. Man of the infected suffered from heart attacks and died. There were further incidents during the 16th century when the mania was at its peak.
There have been numerous hypotheses for the causes of dancing plague. However, it remains unclear whether it was a real illness or a social phenomenon.
One of the most prominent theories is that victims suffered from ergot poisoning, which can cause hallucinations and convulsions, but cannot explain all the strange behaviors noted during the time of outbreaks.
The dancers seemed to be in a trance-like condition, unconscious and unable to control themselves. Throughout the dancing they screamed, laughed, or cried. The observers were sometimes treated violently if they refused to join in. The participants demonstrated odd reactions to the color red, they often became violent on seeing it.
Other explanations suggest the symptoms were consistent of diseases such as encephalitis, epilepsy, and typhus. Or the behavior was simply the result of stress and tension caused by natural disasters around the time, such as plagues and floods.
Then there are theories the outbreaks were all staged, religious cults at the time may have been conspired well-organized dances, ordinary people joined in to relieve themselves from the daily stress and poverty.
Dancing mania appeared to completely die out by the mid-17th century.