I'm Korean and I remember my mom always told me not to turn on the fan when I was sleeping. I felt it was a kind of lesson from parents, and I hadn't doubt it until I heard the objection.
This story has a long history of a century. It's not dying out yet. Most of the older generations still believe it. Young people do not fully believe it, but are not sure it is completely false. Our media say that there is no evidence accoring to experts, but do not say it is completely false.
In fact, it has become less important issue because most people use air conditioner nowaday. Of course I've never seen the news that sleeping person was dead while the air conditioner was on.