You find the strangest stuff on Wikipedia:

Fan death is an urban legend confined primarily to South Korea. The legend states that an electric fan, if left running overnight in a closed room, can result in the death (by suffocation, poisoning, or hypothermia) of those inside. This belief also extends to air conditioners and the fans in cars. When the air conditioner or fan is on in a car, Koreans are apt to leave their car windows open a crack to avoid "fan death".

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The legend is remarkably resilient, and is accepted even by many Korean medical professionals. In summer, mainstream Korean news sources regularly report on cases of fan death, even if more likely causes (e.g. heart attack, gunshot, alcohol poisoning) are evident. [Wikipedia: Fan Death]