Hundreds of children across Japan experienced seizures five years ago. More than 700 boys and girls were taken by ambulance to hospital. 12,000 kids reported symptoms of illness within two days. An episode of the Pokemon cartoon series was to blame for the mass outbreak.

The 38th episode of the first season of the Pokémon animation was called Denn Senshi Porygon and it sparked a medical mystery. An explosion was illustrated by an animation technique called paka paka, which broadcasts alternating red and blue flashing lights for six seconds. Hundreds of children experienced photosensitive epileptic seizures, accounting for some, but not all, of the hospital stays.

Takuya said that at the end of the show there was an explosion and he had to close his eyes. A 15-year-old girl from Nagoya felt tense as she watched blue and red lights flash on the screen. I don't recall what happened after.

The condition is perhaps best understood as the placebo effect in reverse. People can make themselves ill from an idea

The phenomenon was reported around the world. The ministry of health, labour and welfare held an emergency meeting after the producers of the cartoon were questioned. The price of Nintendo's shares fell by 3.2%.

There were 12,000 children who needed medical treatment. The programme was watched by almost five million people. One in 5,000 people has photosensitive sence. The number of people affected was more than ten times the number.

Benjamin Radford, a research fellow at the Committee for Skeptical Inquiry in the US, became interested in the mystery after four years. He says that the investigation had stopped and the mystery faded away. I was curious if I could solve the case.

He and Robert Bartholomew looked at the timelines and found a key detail. It wasn't just a one-night event but instead unfolded over several days and the media reported it.

Orson Welles rehearsing a radio broadcast of The War of the Worlds in 1938

Orson Welles rehearsing The War of the Worlds in 1938. Photograph: World History Archive/Alamy

After hearing about the programme's effects, most of the affected children became ill. The transmission of the cartoon on December 16th caused hundreds of children to experience symptoms of photosensitive seizure, but something else was at play. On the next day, all of the talk was about Pokemon Shock. More children started to feel unwell. This was made worse by the fact that some news shows screened the offending clip. This time, the symptoms were more similar to mass sociogenic illness than photosensitive seizure.

Mass hysteria, also known as mass psychogenic illness, orMPI, is a well-known phenomenon with cases spread throughout history, from meowing nuns and dancing epidemics in the middle ages to an outbreak of uncontrollable laughter in 1962. MSI is a complex and often misunderstood condition that can be spread through social contact. There is a strong social hierarchy in closed social units such as factories and schools. The victims aren't faking or making them up, but the cause is mis attributed. In reverse, the placebo effect is understood as the condition. It is possible for people to make themselves ill from an idea.

There were other cases of broadcast programmes triggering an outbreak ofMSI. There were 22 cases of an unknown virus in the Padre Antnio Vieira secondary school in Lisbon in May of last year. Students said they had trouble breathing, dizziness, and faint. The school was closed as a result of the virus. More than 300 students in fifteen Portuguese schools were affected by it.

Students complained of difficulty breathing, rashes, dizziness and fainting. The school shut down

There was no evidence of the virus beyond the students symptoms. There is no disease that is so specific that it only attacks children.

The strange truth came to light. Before the outbreak, Morangos com Acar had aired a storyline in which a terrible disease had hit a school. While working on an experiment with a virus, a character accidentally released it and students were struck down, the sickness spreading through the fictional school of Colegio Da Barra.

With the end of the academic year approaching and many students stressed about exams, the story had a more dramatic effect on its young audience than had been intended.

A girl hiding behind a chair

The spoof Ghostwatch documentary from 1992. Photograph: BBC

It is more than just the school children who are vulnerable. There was a mass panic in the UK after Halloween in 1992. The War of the Worlds was a radio drama that caused mass panic in the US when it reported a news story about a Martian invasion. Ghostwatch was a live factual broadcast that took a frighteningly sinister turn. The programme was supposed to be about a house in Northolt, west London, and featured familiar faces including Michael Parkinson.

The show began slowly, before ramping up the tension with a series of chilling incidents, the most chilling of which was the live report from the house that was dragged through a cellar door. According to the in-studio expert, the poltergeist was using the broadcast to create a nationwide séance circle, invading the public's homes. Parkinson was possessed by the spirit after the show ended and the crew all fled.

Parkinson's elderly mother was among more than 30,000 terrified or angry callers who bombarded the BBC's switchboard. Heavy criticism of the show appeared in the newspapers the next day. Six cases of children showing symptoms of post-traumatic stress disorder were recorded, and the Broadcasting Standards Commission found that the presence of the children's show's hosts took some parents off guard.

The cases of Ghostwatch and The War of the Worlds don't involve people developing symptoms, which may make them different from mass sociogenic illness. They're in the same place. The panics were related. Fears were legitimised and compounded when uncertainty was present. Many people said they saw and experienced strange phenomena that were not happening. These are examples of mundane events being seen as extraordinary.

People think they would react differently. The people affected weren't stupid, very gullible, or crazy, so it's important to recognise that. We are all capable of succumbing toMSI Next time you are making a decision, remember that. Countryfile all the way through?