Prologe from my book Incubus: Folklore Series Book 3
Sleep Paralysis. It is a not uncommon occurrence where a person wakes in the middle of the night and cannot move. This usually comes with a panicked feeling, accompanied by noises and movement in the room, seen mostly through peripheral vision. It can also come with a heavy feeling on your chest and a shadowy mass on top of you.
Science has explained it all away, claiming that your body is simply locked in place as per usual sleep routines that your body and mind put upon you in order to prevent you from acting out your dreams. Many times, that is the case. But, every once in a while, more often than not, when a person experiences sleep paralysis, it is caused by a malevolent presence that never walked the universe in mortal form.
Shadow people, nightmare demons, dark fairy folk, and even alien visitation are a few things that could cause these nocturnal torments. However, out of them all, the worst you could experience is the assault of an incubus."