That's creepy! It reminds me of a dream that I had when I was younger and it was the worst dream I ever had and exactly that dream was always coming back, sometimes I even had it twice a week. It was about someone breaking into our house, while everyone was asleep. The person always tried to kill everyone. But there was always a different ending, sometimes I wanted to scream, but couldn't, I also never was able to run, even though I tried really hard & before he stabbed me I woke up.
I guess it's not only screaming, but also dying, running for your life and other things that aren't possible in a nightmare..