Known colloquially as “mass hysteria” (which is now considered a non-PC term), it’s one of the most controversial formally named diseases/diagnosis. MPI is basically where multiple people in the same place simultaneously or in rapid succession experience sudden delusions, psychosis, or other mental issues of a similar nature to each other. Notable examples include the dancing sickness in Medieval Germany where people in a town suddenly got a severe urge to jump up and down in the streets, some doing it until they literally died from exhaustion, as well as the laughing sickness of Tanganyika, where a number of children suddenly started laughing uncontrollably.

It’s said to be triggered spontaneously by things like severe collective stress (for example, the stress of living in a medieval town or a country actively pushing for independence from Britan). For some cases, it may also be due in part to exposure to neurotoxic pollutants, like the infamous ergotism that also caused the Salem Witch Trials. It can start with a single person going into psychosis and triggering similar symptoms in people around them who see the strange behaviour.

It also tends to resolve spontaneously after some time, or some cases are resolved by things like exorcism rituals through the placebo effect and the sufferers believing that the “treatment” would help.

I’ve even heard some theories that MPI is responsible for things like miracles supposedly seen performed by religious figures throughout history, or in more modern times, mass sightings of UFOs and paranormal activity.

Do you think this disease is a real thing? Or do all the documented cases have a different underlying cause that we simply haven’t discovered?