Contagious Behavior

In January 1962, three schoolgirls in a small village on the western shores of Lake Victoria started laughing.

Not a casual giggle. Not the kind of laughter that bubbles up during class when you're trying to be serious. This was something stranger—something relentless. The girls, all students at a boarding school in the village of Kashasha, couldn’t stop. Minutes turned into hours. Their sides ached, but the laughter rolled on. There was no punchline. Just the sound of it—shrill, uncontrollable, and contagious.

Within days, other girls began to laugh too. Then more. And more. Teachers were baffled. The headmistress tried separating students, scolding them, even praying over them. But nothing worked. The laughter kept spreading. Some students would fall into fits that lasted over an hour. Others would break down in tears, then switch back to laughter, as if caught between opposing tides of emotion. Some fainted. Some developed rashes. Others ran in fear, convinced they were cursed.

After just a few weeks, 95 students—nearly two-thirds of the school—had been “infected.” With order breaking down and teachers unable to control the chaos, the school was forced to close.

But the epidemic didn’t stop there.

The students went home to their villages, and the laughter went with them. Soon, it appeared in Nshamba, a nearby town where some of the girls lived. A different school—previously untouched—was suddenly overwhelmed. Hundreds of students began exhibiting the same symptoms. Laughter, crying, convulsions. Some were bedridden for days. Others collapsed at school. Again, institutions shut their doors, hoping the storm would pass.

It didn’t. Not for months.

Over the next year and a half, the epidemic touched 14 schools and affected more than 1,000 people, mostly children and teenagers. But it wasn’t just laughter anymore. Some victims suffered skin rashes. Others became violent or mute. A few had memory loss. And through it all, no one could identify a cause. No bacteria. No virus. No environmental toxin. No witchcraft—though that explanation circulated too.

Doctors and colonial health authorities were mystified. They tested water supplies. They interviewed victims. They took blood samples. Nothing.

It would take decades—and the lens of hindsight—for psychologists to piece together what had likely happened.

What swept through western Tanganyika in 1962 wasn’t a medical outbreak. It was psychological. A rare and poorly understood condition called Mass Psychogenic Illness, or what used to be called mass hysteria. It wasn’t the first case in history, but it was one of the most dramatic. And it started, of all things, with laughter.

Mass psychogenic illness occurs when a group of people—usually tightly knit or under similar stress—begin to share symptoms that have no physical origin. These episodes often follow social disruption, fear, or sudden environmental changes. In this case, the village had just gone through a major shift. Tanganyika had declared independence from Britain only weeks before the laughter began. For many young people—especially girls in missionary-run boarding schools—this was a moment of massive upheaval. Cultural, educational, political structures were in flux. The expectations placed on children were high. The emotional pressure? Higher still.

The laughter wasn’t joyful. It was a release valve. And it spread not because people were faking it—but because they were vulnerable to the same invisible weight. Anxiety moves like electricity through tight communities. One spark is all it takes.

But what’s most unsettling is how familiar it all feels.

You can’t help but think of other moments—moments when emotion, not logic, sets the tone. When something irrational builds momentum simply because enough people believe in it. It doesn’t take a boarding school in 1960s Tanganyika. It can happen in a modern office. A neighborhood. A friend group. A country. A market.

The symptoms are different, but the energy is the same: A creeping sense that if everyone’s doing it, it must be right. That not joining in makes you the odd one out. That maybe you’re missing something big.

And that’s where the story starts to echo in our lives, especially around money.

Because if we’re honest, most financial mistakes don’t come from spreadsheets. They come from mood. From the quiet panic of feeling left behind. From seeing your neighbor buy a second house, or your cousin quitting her job to trade crypto full time, or your coworker bragging about gains you didn’t even know were possible. It builds. It spreads. One spark is all it takes.

It’s easy to believe that we’d never fall for it. That we’re the rational ones. Immune to fads, manias, stampedes. But the truth is, when enough people laugh—or buy, or sell, or panic—it gets harder to stand still.

That’s why self-awareness might be the most underrated financial skill out there. Not technical analysis. Not tax efficiency. But the ability to pause when the crowd is speeding up. To check in with your own values and goals before echoing someone else’s excitement—or fear.

The story of the Tanganyika Laughter Epidemic is bizarre, yes—but it’s also a mirror. We may never laugh ourselves into collapse. But we’ll all be tempted, at some point, to follow the crowd.

The question is: when that moment comes, will you remember to stop and ask, Why am I doing this?
Because not every contagious thing is worth catching.