Sleep paralysis along with the cultural influences where they live and the innate primal fear of the dark has always caused people to experience nightmares and abductions.
Like for example, in the Middle Ages, people though that demons were siiting on peoples' chests ,the most famous is the old hag.
I ,too, have experienced it. Once , when I was four years old , I was sleeping in my room until a satan-esque creature was staring at me with its' evil red eyes ,grinning. I was scared enough that I slept with my Grandma and it came back again, but as a shadow. When I went to my room to sleep, a year later, a group of demons were staring at me while I was paralyzed on the floor . I thought I was gonig to die ,then I woke up.
So as I said,it all depends on the culture and the fear of the dark and unknown.