Sleep Paralysis; this is a fairly new subject of research for me but also for most other people. I would say the subject started being researched about 20 years ago, but the phenomenon was allegedly always known through history. People used to attribute it to demons, ghosts and other malevolent entities visiting people during sleep. There are of course also some scientific explanation of why this happens, some more "mundane" explanations. Something to do with waking up during the REM sleep phase. This is most likely caused by sleep deprivation or not being constant in one's sleep patterns. The body in during this phase is paralyzed. It's a natural safety mechanism us humans have, to prevent us from moving too much when sleeping.
Basically sleep paralysis is like a terrifying version of a lucid dream experience. It is all so vivid, and the feeling of helplessness is palpable. I never had intense sleep paralysis before, well, not that I knew of. Although, I do vaguely remember some very short and confusing, mild episodes of it. Once upon falling asleep I distinctly heard someone shouting in my ear (I think it was my name) and making me wake up then I heard breathing when no one was there. And once I reckon I experienced my bed covers and sheets being pulled. But I'm not 100% this happened, because it might have also been a dream, or a dream within a dream. Matter of fact all that happened during my sleep, so it was kind of shocking to experience it for me. This was especially intense for that short time when my brain actually didn't have enough information as to process and classify what was happening to me as a dream or an awake episode, and that made it feel that much more real at for me.
Tonight though, I distinctly remember, I was dreaming that I was in my living room lying on the couch and watching tv, then all of the sudden my body started to shake, it felt so real and powerful, and uncontrollable shaking feeling and I couldn't do a thing, but let it happen. Then I woke up I was in my bed, just in the exact same position I fell asleep in. I heard a child giggling. I watched the top of my bed sheets and cover being pulled up in the air, like half a meter above my head, as I watched, I tried to kept calm and my kept my nerves steady. Instead of feeling scared, I was feeling angry and annoyed.
Then the sheets of my bed suddenly moved by themselves, fell and covered my head, and immediately after at least three of these ghost children were running and jumping on my bed cover, specifically, right above my head, like trying to make me feel scared. I felt none of their body weight, but I saw the sheets and covers getting bent like there were invisible entities jumping on the bed. I remember trying to pull my arms back and I was ready to swing full force with both of them and catch whatever was jumping on my bed or at least try to shoo it away. But surprisingly I couldn't swing my hands at all, I couldn't move them!
I was completely paralyzed, felt so powerless, and remember I couldn't make a sound as well. Then I heard a deep voice that sent shivers down my spine coming from my left side, as I turned to the left to face it, I suddenly and finally woke up super confused and trying to make sense of what just happened. It felt so unbelievably real. Then I started to think and realized that what just happened it couldn't have been real.
It wasn't possible, because of 2 main reasons: I remember in the nightmare my bed sheets distinctly having a pattern, which my sheets do not have and also, in reality, I had my right side of the bed covered with something heavy, so it is literally impossible to lift the sheets and covers so up high above my head without removing that stuff first. What I experienced, it literally couldn't have happened and I'm ultimately glad for that.