Got similar stuff every once in a while. I feel awake and realize my surroundings, but I can't move, can't scream, can't do anything. It's very unpleasant. After a while I can get myself to wake up and it's over, with my heart beating super fast.
Sounds like a big thing, but it's not so much. After such uh... dream..., I feel pretty normal again (I don't have it often, it's actually very unusual anyway). What I remember is, that I once tried to talk / scream for help so that someone wakes me up, but it didn't worked. *This* is the worst bad thing, which is also the reason why I will never ever intoxicate / deafen me fully if I'll have to undergo some operation. My fear is just way too big that I would be awaken, but just can't move. :> (There have been cases like that already)