The Dancing Plague
This strange event dates back to the 16th century in Strasbourg, where somewhere between 50 to 400 people took to the streets to dance uncontrollably for days. About 15 people were dying every day due to exhaustion and heart attacks and many others were taken to a healing sanctuary. Although this phenomenon cannot be explained, there are many theories about it, one of which is the overwhelming living standards of the poor population of Strasbourg.
Explained almost 3 years ago:
https://earthsky.org/space/wow-signal-explained-comets-antonio-paris