I am in the field of Neurophysiology. I'm not sure you're interested in this - or maybe you already know - but I can tell you some things about "sleep paralysis." It's during REM sleep that we dream. Our brain puts out chemicals during REM sleep that paralyze us so we don't act out our dreams. With respect to that, a sleep disorder can result in acting out dreams because the brain is not putting the paralyzing chemicals out, or the brain can also fail to resolve the paralysis when out of REM sleep. That means the paralysis may still be in effect when we awaken. It's usually very brief, but can be scary. The phenomenon is frequently associated with Narcolepsy