And, worst of all, it's impossible to move. This is frightening, I'll agree, but, to the best of my knowledge, there is no danger. If you can move as much as the tip of your little finger, you'll snap out of it. To round out this discussion of dreams, I must discuss night terrors. Night terrors are not nightmares.
Nightmares are simply dreams that take a frightening twist.
They occur during REM sleep. Night terrors, on the other hand, occur during Stage 4 sleep. This is the really deep sleep. The dreamer awakens often screaming, sweating, disoriented, and obviously terrified. The problem is he or she usually cannot remember what has been so frightening.