I mostly suffer from the audio-only form of sleep paralysis. It's... unnerving. Scary or terrifying would be a wrong word to describe it though. It used to be that, but it moved towards something worse after a while.
The first time I ever got sleep paralysis, at least as far as I can recall this was the first time, I heard the neighbors upstairs fight. It was a serious fight. Stuff got thrown around, heavy objects made their way to the floor. There were screams and shouts, I heard things break. Then there was a final shout and a loud thud. Shortly after, footsteps made their way to the hall. Then they took a staircase down, making their way to my hallway, into my house. There wasn't supposed to be one, but at a time like that, in a paralyzed state and still dazed because only just woke up, you don't think about that sort of thing. The footsteps made their way to my door... and I snapped out of it.
I wasn't entirely sure if what I heard was real or not. I thought I had gone insane. After a while, I put it aside as a dream, despite the fact that I knew that I had been awake during it.
Believe it or not, that was far from the worst experience I've had with it. That one was easy, there were no neighbors upstairs, that place was empty. There's no staircase in the hallway leading up. It was illogical for that to could have happened. Thinking about it that way, I was less shocked of the thing. Even when it happened again. Twice over.
Still, nothing compared to the turn it made later.
See, my problem with sleep paralysis isn't so much the fear of the unknown, or weird sounds I can't identify. They're usually not even that violent. The real unnerving part of it is that it keeps tying into what's on my mind. What's wrong. Or often enough, what I had just dreamed. Often enough, those dreams are damn realistic as well, as far as dreams can be such. As nice as a lot of the posts in this thread are, they're approaching it from the wrong angle.
Imagine, at the point my sleep paralysis problem started, I was not experiencing a good part of my life. In fact, my life was a complete mess. I drank a lot. Slept at odd times. Had constant stress problems because of my shitty job. Never saw my family. Didn't have any friends to count on. You name it, and it was wrong. House was a complete mess as well. I nearly got kicked out when the landlord saw the state it was in.
Okay, got the mental picture? I dreamt my mom found my address and decided to come visit me, with my life being what it was and the house being in the same state as it was in my waking life. She saw it, got upset. She got hysterical. Ran around the house yelling and screaming. Then sleep paralysis kicked in. I was awake, couldn't move. And I could hear her going through the house, yelling and screaming about what a complete disgrace I am. Throwing stuff around the house, tearing the place down.
I was a complete mess for the rest of the day, even though I knew it wasn't real. It hadn't happened, and still it stuck with me.
Then there was the time at my old house with my old roommate. We had a fight the night before. Sleep paralysis led me to believe she had stood in front of my door crying. Punching the door repeatedly. Asking me why I did all those things. I hadn't done anything. The problem that we fought about was both our faults. I was too afraid to raise the subject the next day. Good thing I didn't, she'd have thought I had gone insane.
There's been one instance in which I saw things. It wasn't as bad as the audio ones. Sure, a witch was pressing me down with one hand and demon dogs ran rampant through my room... But that sort of thing just doesn't happen in real life. It was a lot easier to brush that one aside as a dream than anything else. It didn't make me see or fear people I actually know or force me to see them in a light I'd rather not.
Last night I had sleep paralysis. First time in over a year that I suffered from it. Not really happy that it came back. I was hoping it'd stay away.
What happened? Roommate was smashing the place because she was angry with me. Then she headed towards my door and kicked it, loudly. Then nothing. I snapped out of it.
I immediately knew it wasn't real. It's not realistically viable for it to happen. I could brush it aside easily enough... Still, I don't like the idea of hearing or seeing sides of friends like that, real or not. It's unnerving. It hasn't really happened, but it feels like it did.