This sounds so familiar to me. It does not happen so often anymore but there was a time where it was happening to me nightly. I would have "demons" in my dreams and I would simply be unable to move to help myself. All I can say is that I identify because it feels so real. I remember my relief when I was finally able to wake up properly and of course I did not go back to sleep. Some meds over the years has made it worse so that could be an underlying cause if you are on meds. Demons frequent my dreams too often and I have never understood why.