Have you ever had a dream where you are trying to scream and nothing comes out? I have these often, and upon waking I always have an uneasy feeling. Like something from the unknown has come to haunt me and I can't seem to communicate with it. The strange thing is, not only can I not speak during the dream, I can't move nor do I ever see what it is that is frightening me.

Recently I have read the reason we can't make a sound or move during these dreams is because we are actually in a paralyzed state (this happens during the dream cycle to prevent us from acting out our dreams). These dreams are called "Intruder Dreams". It is during these types of dreams that we feel frightened, because we are faced with an intruder and are unable to scream or lash out.