…because it used to happen to me when I was a little kid. The old witch on my chest, the whole deal. Later on, in my late teens and early twenties, I had problems with similar hypnagogic dreaming, the evil entity in that case being some kind of screaming demon I could never see. (Always over to my left, as in the experience of the author of the linked article.)
My mom taught me a trick to stop it, when I told her about it – it used to happen to her, too.
It’s terrifying. I can believe it could kill somebody. And a new book suggests it may be part of the cause of the mysterious sleeping deaths of Hmong immigrants in the 1980s.