I've heard this before, that scarey images are concocted by the brain during sleep paralysis to produce things like the night hag, or things sitting on people's chests which strangle them, because the brain is trying to make sense of the scarey situation of sleep paralysis which it feels helpless against. The problem I see with that is that in my own dream or experience of sleep paralysis, I saw an entity before I became scared. In fact, I thought it might have been a sleep walker at first, and I wasn't scared. I didn't realize that I was paralyzed until after I saw it up close, knew it wasn't a family member and tried to attack it. Knowing that I couldn't defend myself from what I already saw was what was scarey. The order of events doesn't seem to match the explanation.