This is something I'd normally go to eHealth for, but we all know how that went! Anyway...
I believe I have experienced sleep paralysis. The few times I've experienced a lack of movement when asleep have both been what could be defined as "naps" (which is listed as one of the triggers). I would sometimes take naps in the student union at my college, lying sideways, curled up on a couch with my friends all around. Sometimes in this napping state, I would feel partially awake, as if in a heavy haze. I would not be able to move. Breathing was also difficult and shallow, though I didn't seem to be low on oxygen; I simply thought I should be breathing more but didn't apparently need it. I flt dizzy and light, almost like I was rotating or floating. Sometimes my body would feel numb or jut like it wasn't there. No effort to move worked, and I often either fell back asleep, or was jolted out of this state by someone moving or stimulating my brain in some other way like talking to me.
I don't have any hallucinations though, and normally don't feel any terror or even fear. Frustration and bemused interest is normally all I feel.