Mass hysteria is an actual thing. It starts with an instance or two of conversion disorder, which is when psychological trauma triggers physical symptoms like hiccups and tics. Then, that conversion disorder becomes contagious.

The conversion disorder becomes "contagious" due to a phenomenon called mass psychogenic illness (MPI), historically known as "mass hysteria," in which exposure to cases of conversion disorder cause other people—who unconsciously believe they've been exposed to the same harmful toxin—to experience the same symptoms.

There have been numerous cases of this throughout history, but the most widely known instance came when 20 women were hanged in the Salem Witch Trials.

Though it hasn't been officially declared MPI, two dozen young women at a school in Massachusetts began experiencing such symptoms early in 2013. And, as that case progresses, experts look to a recent case in Le Roy, New York, where a 35-year-old woman who didn't have direct contact with the girls afflicted somehow managed to develop the tics associated with MPI. The catalyst? Social media, probably.

Marge Fitzsimmons, a 36-year-old nurse in town, also "caught" the disease. Bartholomew said that it's not unheard of for one or two adults to be affected, but he cannot recall any cases like Marge's, in which the adults were not intimately involved with the children suffering from the malady. Marge said that she knew about what was going on in town mainly through Facebook postings.

Catching an illness through Facebook sounds wonky. But the contagion of hysteria relies, among many things, upon the unconscious interpretation of what is suggested to us. Fitzsimmons did not even have to be in physical contact with the other girls to "catch" their disease. Marge encapsulates the power of social media to penetrate and trigger actions of the unconscious mind. She marks "a historical shift in terms of the trigger for people being affected and sucked into these cases," Bartholomew said.

Laura Dimon has published a lenghty piece over at The Atlantic that examines the cases in Danvers and Le Roy, the specific case of Marge Fitzsimmons, and the possible effect social media can have on the resurgence of MPI in the Western world. It's informative, harrowing, interesting, and worth 15 minutes of your Wednesday. [The Atlantic]