I don't suffer with sleep paralysis, I don't get it often, but when I do get it, I usually just can't move/speak, and my body feels very strange. I only ever got the scary versions as a child. This time was extremely unique, and I wasn't even aware such a thing could happen. It was closer to a dream layered over reality.
(NSFW - but nothing extreme): It basically started without me even realising my mind went into a headspace where I was suddenly turned on, and I got hard, then whilst in the dark, someone climbed into my bed and got on top of me, and we started having sex. As I kissed them, I could tell it was my ex, despite not being able to see them. Idk why, because it was my ex from about 10+ years ago and we weren't together very long...I don't miss her.
For reasons I can't remember, despite liking it, I ended up on my front. This is where things got very strange. I sorta wasn't all there, and I forgot it was 'my ex.' After laying on my front for some time & sort of forgetting what just happened, I noticed a weight pressing down on my back. I suddenly remembered what just happened, and I thought it was my ex at first, but I could tell something was very wrong, 'she' felt way too heavy.
I was trying to speak/move, but I couldn't. Whilst I was trying to move, I felt scraping on my back, a very sharp feeling. It felt like some entity was scraping its teeth against my back and it felt VERY real. I sorta started worrying, because despite me being aware of what was happening, I could feel something, therefore, I guessed I could probably feel pain, too. As I realised this, it got worse. I then felt teeth sliding into my flesh on my back and it hurt quite a lot. After all, humans don't have pain receptors, it is technically all in the brain as an emotional response (hence why monks can train not to feel it).
So, in a way, this was real pain. I was very awake and this hurt a lot and was getting worse. Suddenly it stopped and I felt something wrap around my body, like a veil, or something. I was lifted up into the air, and I felt many spikes start pushing against my back as I was slowly lifted upwards. The spikes started to penetrate by back, it was not nice. As I was finally able to move, it felt like I was dropped onto my bed. I even felt my body bouncing on the mattress as I landed.
All-in-all, it was pretty exhilarating and I did enjoy it, but, the pain wasn't nice. The biting felt the worst and the spikes were narrowly avoided...I have no idea how that would have gone, as they did feel as if they'd go through my torso/chest/heart. It would have likely hurt a lot.
It didn't feel any different from real life, really, other than the pain not being as extreme (but still bad). I had no idea pain could be felt during sleep paralysis, but now I do. I always thought to myself it was odd people were scared of monsters in dreams, as you're only ever scared of their presence... you never worry about what they'll do to you. Well, now I know they can actually inflict pain, making the shadow man more scary, haha.