Hmm there are four issues I'll discuss. Your inability to have moved, the ghost that you mentioned, regret, and a personal experience.
Sleep Paralysis
I'm not sure if you are aware of it, but sleep paralysis is a relatively normal thing. It doesn't occur at a 90% rate or anything, but it's not all that unusual. Sleep paralysis is actually said to be caused by sleeping on your back.. so since you were laying on your back, that might have one thing to do with it. Additionally, some say it's a psychological thing. I don't know for sure about that, but yeah, it's something I looked up in the past.
Many people have experience(s) with it, myself included. So, unless you already knew about sleep paralysis, you can rest easy and avoid worrying about that.
The Ghost/Demon
As for the ghost/demon thing, yeah, that's kinda weird. My sister... whom I no longer see, mentioned a similar dream. Someone stood at her bedside with a weapon in hand. I don't remember it completely because it was so long ago and it wasn't even my experience, but she told me about it. I guess we tend to see scary things like that at night, when in that status (sleep paralysis).. perhaps the ghost you saw was something you have a fear of. Haha, I sound like a psychiatrist.
Regret.
You shouldn't feel regret for things like hurting someone's feelings. You said you'd regret it forever if you did. Everyone gets hurt sometimes so, if you were serious about what you said, you should probably take it easy. As you said, it would be an accident too. So even if others don't forgive you, you should forgive yourself.
Personal Experience
Though I never saw someone standing at my side, or anything like that, I have found myself in a state where I couldn't speak, move or anything. However, I'm almost certain that I was awake and I wasn't dreaming or anything. It's pretty freaky how that happens to people.
Anyway, that's all I have to say for now. :)