When I was about 21 I read about training yourself to do lucid dreaming by repeating to yourself that you would remain in control of your mind as you fell asleep. Within just a few attempts I was successfully lucid dreaming, although with somewhat limited control. I was hoping to keep practicing and get better at it.
But shortly after this success, I experienced sleep paralysis for the first time ever. It was absolutely as horrifying as everyone says it is. I couldn't move, but my eyes were open, and my "sleep paralysis demon" took the form of the black drape I had covering the window in my bedroom, which my brain was interpreting as some huge and pitch black entity looming over my bed while I couldn't move.
I stopped trying to lucid dream, but now I still get sleep paralysis once in a while, like a couple times a year at this point. The last time it happened I was sleeping next to my girlfriend, I couldn't move and I kept thinking I was hearing someone loudly stomping down the stairs to our bedroom. I managed to make some extremely strained, high-pitched but not loud "screaming" noise - sorta like when you try to scream but keep your throat closed but like... wrong - and my girlfriend was able to shake me awake.
She knew about my sleep paralysis because it happened not long before that and I told her about it, and so she was ready to help me, but I still thought she would be more unsettled by the very disquieting noise I was making, lol.
Anyway yeah that shit sucks, do not recommend.