My experiences with sleep paralysis began with some of what you guys have mentioned: sort of strange, creepy visions. The idea of another presence in the room. One that I remember specifically was a sort of dark, faceless woman. Kind of like a witch or something. Weird. Real weird.
The other day I had the sensation that a dog was in my bed next to me, sort of snuggled up next to my shoulder. So that one wasn't exactly scary, but it's so odd because at the time you are just COMPLETELY convinced that it's actually happening. And I wake up and there's no dog there.
For the most part now it just centers around that crazy feeling of being totally frozen and mostly helpless. It really feels like a seizure. And over the past few years the pain or sensation of paralysis seems to be really sharp and focused on one specific part of the body. Often times it's a part of my chest, like even my heart, that gets that sharp seizure feeling. And that's scary. Sometimes it's my head, even.
I've never really talked about this stuff at length with anybody before this. I'm glad that other people have/have had similar shit happen.