You can catch the ‘nocebo’ effect from family, friends – even social media. But what is it, actually?

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In 1998, shortly after arriving for work, a Tennessee high-school teacher reported a “gasoline-like smell” and feeling dizzy. Soon after, many students and staff began reporting symptoms of chemical poisoning. Some 38 people had such extreme symptoms they were kept in hospital overnight.

Yet investigators didn’t find any evidence the school had been contaminated.