While still in my residency training program, I was watching the news, and a story caught my - a bunch of grade school kids had been hospitalized because of a mystery illness.

Outbreaks of mystery illness are more common than we think - often a physical culprit is discovered, but psychological stress and are sometimes the cause. Epidemics of hysteria have been recorded as far back as the Middle-Ages and continue to strike today. Most often, the outbreaks afflict children and , girls more than boys, and fainting and hyperventilation are the most common symptoms. Occasionally the illness persists for days; but usually, once the afflicted crowd disperses, symptoms tend to disappear, probably because they are only contagious when new victims observe others falling ill. Rumors about the cause of these outbreaks tend to spring up throughout the communities.

In all the mass hysteria episodes I've studied and written about over the years, the lingering question for me is why they don't happen more often. The essential ingredients - groups under psychological and physical stress, often hungry, tired, or both - come together almost daily all around the world. So what is that ultimate trigger that pushes some people over the edge and let's their minds take over their bodies en masse?

When I investigate a mystery illness, many victims and their families become defensive because they think I might be accusing them of having an illness that is "only in their minds." It makes sense when you think about it from the victim's point of view. The physical symptoms are experienced as real, and when they strike, even if the victim is swept up by the excitement and anxiety of the crowd, how could their real physical experiences - hyperventilation, fainting, nausea, stomach pains - be the result of anything but an actual physical illness?

Some people are more likely to endorse a far-fetched or outlandish cause for their illness than to consider the mind-over-matter theory. Examples of bizarre explanations for mass hysteria have included a "phantom gasser" that Mattoon, Illinois, residents believed was spraying poisonous mist into the bedroom windows of teenage girls, causing nausea, vomiting, and burning sensations in their mouths and throats. In the early 1950s, when people in the state of Washington were nervous about nuclear testing, many believed that cosmic rays or shifts in the Earth's magnetic field were causing previously unnoticed windshield pits or dings in their cars. Some even blamed it on "super-natural gremlins." Although this is an example of collective delusion rather than mass hysteria, it shows how a worried group can over-interpret physical phenomena that were already there but went unnoticed before the spread of anxiety.

When we face uncertainty, our minds crave explanations. If we have no way to account for symptoms, we feel out of control and our escalates. And, if we learn that our own minds may have caused these very real symptoms, we tend to feel more anxiety about what our minds might do next. People may worry that their brains are possessed by some outside spirit, or perhaps a poltergeist has taken charge of their . They'd rather latch onto something like the mysterious poisonous water theory.

Psychosomatic specialists have come up with additional physiological explanations for some of the symptoms of mass hysteria outbreaks. When people get excited and scared, they may hyperventilate or start breathing too quickly; thus, exhaling too much carbon dioxide. Low carbon dioxide levels in the body cause muscles in the extremities to spasm, which can explain the numbness, tingling and muscle twitching that some victims experience. If the carbon dioxide depletion is treated by simply breathing into a paper bag, the symptoms rapidly disappear.

In a heightened state of anxiety, victims often notice and misinterpret normal physical sensations. A gurgling stomach can be mistaken for a sign of food poisoning. And if others around you grab their stomachs and fall to the floor, your fear level may heighten, your knees might buckle, and you may fall to the floor as well. The sheer force and power of group dynamics tends to take over, and people get swept up in the symptoms of the crowd. The social hierarchy of the group can also play out in the spread of symptoms. If the "popular" girls faint first, the less-popular will likely follow their lead.

In the "Fainting Schoolgirls" incident from my new book "The Naked Lady Who Stood on Her Head: A Psychiatrist's Stories of His Most Bizarre Cases," I was investigating a sudden outbreak of illness in a suburban grade school. The kids were rehearsing a performance, when suddenly 30 of them grabbed their stomachs and fainted. The principal told me that it started with one popular child who fainted and suddenly the rest of them went down like dominoes. The health department couldn't find a cause and gave the "all clear," but the community was in an uproar. The school seemed to be blocking my efforts to get to the bottom of things, and the parents took offense that a psychiatrist was suggesting that their kids might have had a psychosomatic illness. I nearly gave up my study until I attended the actual show - a little worried that the outbreak might recur - when one of the mothers sought me out and supported my theory of mass hysteria - she was convinced that her daughter's physical symptoms were in fact psychological. My subsequent research proved my theory that when out, the mind can make the body sick, and in a group setting, it can really get out of control. Mass hysteria can strike anywhere, anytime.

See my new book, "The Naked Lady Who Stood on Her Head: A Psychiatrist's Stories of His Most Bizarre Cases."

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Copyright Gary Small, M.D.