If you want to challenge your deepest notions about human reality, read "The Dancing Plague" by John Waller.
During the Middle Ages, there are very detailed records of a strange mass mania that erupted amidst the horror of everyday life, back then. People would start dancing until they passed out or died. Apparently, this also happened in Madacascar once.
After reviewing all the evidence, the author concludes that it was NOT a physical disease or the result of poisoning like ergot. It was mass hysteria and belief that caused people to imitate their shaking, twitching peers and fall victim to the "Dancing Plague" - rather like a sort of "Holy Roller" meeting writ large.
The final chapters of the book discuss the power of collective belief and obsessive action. A very strange but well documented book.