It is a very interesting and profound topic. It happens to me personally and the truth is that the first time I suffered from paralysis I had to make an effort to calm down because the fear I felt has been one of the worst in my life.
Once it happened to me that sleeping, I suddenly had an episode of those "lucid dreams" with the character of the shadows that you mention, and it was worthy of the worst horror movie: I was lying in bed and suddenly I felt a FAIR presence on my face, all black, looking at me face to face, millimeters away, floating there.
I think I can consider myself a brave person, after having survived that. Hahaha Very cool and interesting post, congratulations!