I also wanted to say, Night Terrors and Sleep Paralysis are not the same thing, although they may occur in the same person. Night Terrors are when someone starts screaming and thrashing (obviously NOT in REM, as you can't move in REM) and is difficult to waken. When someone does awake from a Night Terror they usually don't remember any of it, or remember a dream "fragment" opposed to a full dream superimposed on reality.
Sleep Paralysis, as I talked about and linked in the other thread, and it occurs during REM, when the person has some wakefulness but a feeling of malevolent presence, paralysis, difficulty breathing, odd sounds, along with extreme fear etc. They are caused during differing cycles of sleep (Night Terrors in Deep NON REM sleep, and Sleep Paralysis during the transition between REM and waking.) and cannot occur at the same time. Although, some people will
scream when coming out of a Sleep Paralysis episode, it is not the same as Night Terrors. Night Terrors are more common in children, while SP is more common in teens and people in their 20s through 40s.