In a complete opposite of the South Korean fan death myth, it turns out astronauts actually NEED to sleep next to a ventilator fan while they're in weightless orbit. Why? If they don't, they might suffocate in their sleep.
The reason is because warm air doesn't naturally rise when there's no gravity. If you don't have a way of circulating air, then the carbon dioxide you expel when you breathe can form a bubble around your nose. Eventually, the air available to you wouldn’t have enough oxygen and you would die.
Learn more about what astronauts have to go through to sleep at the source.