If everyone is laughing, that’s usually a sign that things are going well. Not so in the case of a peculiar and unexplained phenomenon that hit Eastern Africa in the 1960s. Plenty of people were laughing, but there was nothing funny about the Tanganyika Laughter Epidemic.

It all started on January 31, 1962. The village of Kashasha on the western coast of Lake Victoria seemed an unlikely place for anything out of the ordinary. Students at the mission-run girls boarding school started what seemed to be a typical day. It was then that something really strange happened.

It began with three girls. They started to laugh. At first, students and teachers alike assumed it was a case of childish goofing off. When the laughter continued unabated for hours, school officials became concerned. When the symptoms started to spread, the concern grew to alarm.

The uncontrollable laughter spread throughout the school, affecting 95 of the 159 students. In some situations, the laughter gripped the girl for a few hours. In the most extreme case, it didn’t let up for sixteen days. Teachers attempted to conduct their lessons despite the distractions for six weeks, but the school was forced to close on March 18.

The situation grew even more dire when symptoms began to show in the nearby village of Nshamba. Throughout the months of April and May, uncontrollable laughter gripped 217 more victims. In June, the peculiar malady spread to the Ramashenye middle school, near Bukoba, affecting 48 girls.

Over the course of eighteen months, the laughter epidemic continued to spread. As victims struggled to control themselves, the fits of laughter also triggered fainting, flatulence, difficulty breathing, skin disorders, crying, and screaming. A total of fourteen schools were closed and as many as 1,000 people suffered the effects of the inexplicable illness.

Then, as suddenly as it appeared, the laughter epidemic stopped. A year and a half after the first victims showed symptoms, the epidemic vanished, leaving the people of Tanganyika to pick up the pieces and try to return to a world that paradoxically was happier because of less laughter.

Christian Hempelmann of Texas A&M University has studied the laughter epidemic and speculates that it was an example of mass psychogenic or sociogenic illness, triggered by high-stress settings. Since the illness primarily affected young girls in boarding schools, the stress factors may have included the unfamiliar expectations imposed in the British-run schools, as well as political uncertainty arising out of Tanganyika’s independence, which occurred just one month before the outbreak.

One thing the laughter epidemic does not speak to is the contagiousness of laughter. If you happen to be near someone who starts laughing because something is actually funny, it is common for you to start to giggle, as well. That is an entirely different phenomenon than the stress-induced, days-long laughing fits experienced in Tanganyika.

While rare, the spreading laughter epidemic of Tanganyika is by no means unique. Similar incidents have been recorded in Kosovo, Afghanistan, and South Africa. In all of these situations, the outbreaks occur among those who are burdened with extreme stress without any other means to respond. Laughter fits are most likely to show up in young people. Girls are affected more frequently than boys. “It has to express itself bodily, that gives the person a way to say, ‘I’m suffering; something is going on; I’m not just depressed or withdrawn,’” explains Hempelmann.

Laughter is one of the body’s best mechanisms for dealing with stressful situations. An entire field of research, gelotology, has developed around studying the benefits of laughter. Practices such as humor and laughter therapy, laughter meditation, and laughter yoga begin with feigned laughter, developing it into the real thing. Laughter has been shown to release endorphins, reduce stress hormones, and improve physical and psychological health.

If the body is unable to cope with stress in any other way, it will force itself to laugh at it. If there is a lesson to be learned from the laughter epidemic, it might be that we all need to lighten up and find something to chuckle about from time to time.