I have a large scar on my arm from a similar incident in my youth. Possibly brain damage as well.

I awoke to a shadowy figure standing over me, so I did what any reasonable person would - I lunged out of bed, screaming incoherently, and tried to tackle it. It was unfortunately imaginary, unlike the hard, wooden floor. I poorly performed a shoulder roll and scraped my arm along one leg of my bureau, tearing the skin from my elbow halfway to my wrist, and cracked my head into the wall.

My parents found me incoherent and covered with blood. A trip to the hospital yielded a diagnosis of a mild concussion and an avulsion wound too ragged to be stitched back together.

i get sleep paralysis if i sometime sleep on my back, and only if i was exhausted the day before.

So when I was a teenager I used to have a desktop computer in my bedroom, with desk, chair and all, the bed was against the far wall from the door, with the desk in between. One night I woke to a dark figure bending down over me while I slept, and my instinct was to punch it! And I kinda hurt myself by hitting the metal frame of my computer chair which I had somehow rolled next to the bed without noticing, with a black hoodie draped over it.

I can't sleep on my side because, as a kid, I was sleeping with my back to a window and had this overwhelming horror where I just KNEW these humanoid creatures were looking at me through the window. I had this feeling they were going to inject something into me that would collect together into a single mass and come out of my like a chest burster. As stupid as it was, I was a 12 year old who was horrified of what his mind told him.

Ah I see you've met the sleep paralysis demon too.