Nausea. Dizziness. Vomiting. Such were the symptoms experienced last month by more than 1,200 employees of a yarn factory in the Chinese city of Jilin, according to a report in the New York Times.
But even as the workers flooded nearby emergency rooms, Chinese health officials quickly attempted to defuse concerns. While the stricken employees say their illness stemmed from toxic fumes from a nearby chemical plant, the officials maintained mass hysteria -- an outbreak of similar psychogenic symptoms among a group of people -- was to blame.
Although officials are ready to pronounce the symptoms in Jilin psychogenic, others are not ready to believe that. Incidents of mass hysteria, or mass psychogenic illness, have several classic characteristics. But differentiating between it and cases of widespread illnesses that have an organic cause can be difficult, and often the designation is made after the episode has passed.
"It's very possible that it could be an epidemic of hysteria," said Dr. Gary Small, a professor of psychiatry at UCLA and expert on mass hysteria. "It's a phenomenon where it's mind over matter. The mind makes the body sick. It's also the power of the group over the individual."
The overriding characteristic of mass hysteria is the lack of a clear cause, such as an infection or a chemical, something for which a doctor could test. Other important features include a stressful environment, transmission by sight or sound and higher incidence in women.
The physical symptoms of mass hysteria are very real, and experts say they should be acknowledged as such.
There are many documented cases of mass hysteria in medical literature, most occurring in insular communities, such as a school or a workplace. In the past, these have been cases of widespread rashes, itching, scratching or nausea from a perceived odor.
"People start to over-interpret their own physical sensations," Small said.
Given that the global mental state is concerned with economic and health stressors, such as the swine flu virus, Small added that he was surprised there have not been more cases of mass hysteria recently.
Other famous cases of mass hysteria include the Mad Gasser of Mattoon, in which an unknown person was said to be responsible for a series of gas attacks in Botetourt County, Va., and Mattoon, Ill., during the early 1930s.
An episode of the radio drama "The War of the Worlds," adapted by Orson Welles' Mercury Theater from H. G. Wells' novel, triggered another bout of mass hysteria in 1938 when it aired -- this one non-medical -- as it led listeners to believe an alien invasion was imminent.
Not everyone may suffer psychosomatic symptoms. In Jilin, for example, toxins used in the nearby chemical factory are drawing ire from the community as are the carbon monoxide, hydrogen sulfide and nitrogen oxide being vented as waste.
"Within the population, there may be a subset that actually has the disorder caused by the [causal] agent," said Dr. Greg Fricchione, associate chief of psychiatry at Massachusetts General Hospital. "That stuff will make you sick. Carbon monoxide poisoning, for example, at certain levels will cause a variety of symptoms, some of them neurological."
But physical symptoms can be transmitted from person-to-person in small communities by seeing someone suffer or even from hearing rumors of illness.
"It's the reason why [mass hysteria] can spread almost like an infectious disease," Fricchione said. "If someone hears or sees a person with significant or severe symptoms, and if that is accompanied by a sense of risk transmitted by word of mouth or observation, the minds of those people will process that information in unison. ... A belief sets in that something terrible is going to happen to them."
In cases of community-wide illnesses, Fricchione said determining mass hysteria depends on the evidence. Public health officials investigate at the community level to determine a common cause while doctors who see patients individually might try to determine what disease process could result in the symptoms people are experiencing.
"But when people start to develop symptoms without the [causal agent], that makes it even more complex," he said.
Melissa Lenderman contributed to this report.