When U.S. diplomats in the Chinese city of Guangzhou recently started reporting strange, inexplicable symptoms of unknown origin — and which seemed to be spreading among State Department employees — I was reminded of a similar “mystery illness” that I spent some time researching a few hours south of Guangzhou, in a village called Fuhu.

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One afternoon in May of 2004, a third-grade boy at a local school in Fuhu reported feeling that his genitals were shrinking. He panicked, ran home, and his parents fetched the local healer — an 80-year-old woman who had seen this sort of thing before: In 1963, she said, around the time of the Great Leap Forward, an “evil wind” had blown through the village and many people were struck by this illness known as “suo-yang.” She treated the boy by traditional means and he recovered quickly.

Two days later when the school principal learned of the incident, he gathered all 680 students in the school courtyard and, according to a report by Dr. Li Jie of the Guangzhou Psychiatric Hospital, “explained to the students in detail what had happened, and warned them to be cautious, and to take emergency measures if they experienced similar symptoms.”

Within two days, 64 other boys were struck with suo-yang, which in its epidemic form, is referred to in the scientific literature as a “mass psychogenic illness” or a “collective stress response.” The Fuhu case was a textbook example of how such an illness can spread through a group of people, and the headmaster did the worst possible thing by explaining the symptoms in detail and assuring students they were in danger. He all but caused epidemic.

Fourteen years later and a few hours north, American diplomats in Guangzhou repeated his mistake. While the two episodes might not seem related, to people who study mass psychogenic illnesses, the parallels are clear and there is little mystery involved. The key difference is that when this happens in a school, the consequences are minor. When it happens in an embassy, there are geopolitical costs.

We saw this two years ago in Cuba, where several diplomats working at the U.S. embassy in Havana were struck with inexplicable symptoms including headache, dizziness, ear pains, and hearing problems, which the State Department dubbed “health attacks” and which were speculated to have been caused by a “sonic weapon.” The victims were also said to have changes to their brains’ white matter that indicated head trauma, but this claim was greeted with skepticism by neurologists who study “functional neurological disorders,” which can show similar changes.

Now the same process is beginning in China. This is how these epidemics work: In late May this year, according to The New York Times, one U.S. government employee reported, “subtle and vague, but abnormal, sensations of sound and pressure.”

Next, U.S. officials alerted other employees to the condition and sent an email that said, “While in China, if you experience any unusual acute auditory or sensory phenomena accompanied by unusual sounds or piercing noises, do not attempt to locate their source. Instead, move to a location where the sounds are not present,” according to Reuters. They also advised people to seek medical attention if they had any “unusual ailments,” The Times reported.

Predictably, other diplomats soon started experiencing (or recalling) such symptoms, which resembled those in Cuba: headaches, sleeplessness, nausea, etc. One family of four was evacuated after the parents started exhibiting “neurological symptoms” and “a number of individuals” were sent back to the U.S. for testing.

Regardless of their origin, both suo-yang and the “mystery illness” belong to a class of conditions that are difficult to discuss, because they do not easily fit our idea of illness. Some are considered cultural syndromes, while others are referred to as functional neurological disorders. They can affect everything from hearing to cognition to motor control, and most have no simple, mechanical cause, despite their clear physiological impact (as witnessed in the 2011 case of the twitching girls in Le Roy, New York). Instead, they bridge the gap — or close the loop — between the mental and physical, bio and the psycho. They exist at the nexus of narrative and neurology.

Even if there is no sonic weapon, or genitals are not truly shrinking, these conditions are all quite real to the sufferers, just as depression and anxiety are real, and whose sufferers also exhibit “neurological symptoms.” Most of the time they resolve quickly, though in some cases they can persist and cause ongoing problems. And when a group of people have a general knowledge of the illness, a belief in its power, and fear of its contagion, they can become epidemic.

Consider the case of Hainan Island, several hours south of Fuhu, where in 1984 and 1985, an epidemic of suo-yang started and moved from village to village, lasting nearly a year. Rumors spread of a “fox ghost,” sometimes disguised as an old woman roaming the land, collecting penises in covered baskets she carried on a shoulder pole. It was said that two young men approached her and told her to uncover the baskets, and when they looked inside, they saw that the baskets were filled with penises and died instantly of fright.

That epidemic was estimated to have affected between 2,000 and 5,000 people in the region. According to researchers from the Guangzhou Psychiatric Hospital and other institutions, older Hainan residents recounted prior epidemics in 1948, 1955, 1966 and 1974, and concluded that traditional beliefs made suo-yang, “possible,” then “familiar,” then “real.” A subsequent study by cultural psychiatrist Wolfgang Jilek showed that 100 percent of the victims had prior knowledge of suo-yang, and 100 percent also had a “fear of death” from it.

Fear, along with “sociocultural stress,” are thought to be important factors. As Dr. Li wrote: “When a group of young people, particularly schoolchildren or factory workers, encounter a common tension or stress, and there is no proper channel to deal with it, it tends to induce the occurrence of a mass, shared, contagious, emotional group reaction, usually in the form of mass hysteria, namely, the collective occurrence of fainting, emotional turmoil, or conversion.”

Such stress may not always be required, but it does often precede such epidemics. And a strong case can be made with the mystery illness in China. Certainly, there is no shortage of collective stress in the State Department these days. And just as certainly, people are sharing stories about secret weapons and sonic attacks in Cuba, making such an attack seem possible, then familiar, then real.

The fact that U.S. diplomats likely experienced mass psychogenic illness is not a mark of weakness, ignorance or lack of civilization. It’s part of being human. We suffer, and we tell stories to explain our suffering. Stories are contagious and more powerful than we have appreciated. They can feed back into our physiology in ways we’re just beginning to understand.

But when the stakes are high, and our perceived source of suffering is invisible — be it an evil wind, a fox ghost, or a sonic wave — we owe it to ourselves to look very closely at the stories we’re telling ourselves. The real mystery is that we haven’t learned this yet.

Frank Bures is the author of “The Geography of Madness: Penis Thieves, Voodoo Death, and the Search for the Meaning of the World’s Strangest Syndromes.”