Night terrors

Parasomnia that typically afflicts children between the ages of two and five, although a small percentage of adults also suffer from them.  A person in the throes of a night terror will often sit up in bed and scream, eyes wide open.  However, a night terror is not a nightmare.  They do not occur during REM sleep, but rather during very deep sleep, so there is no accompanying dream content.  It is very difficult to wake the subject up in the middle of the episode, and usually the subject will have no recollection of the terror when awake.  Research suggests that in a night terror, the primitive parts of the brain--emotion and basic motor skills--are aroused, while the higher thinking functions remain asleep.   

Source:

Dement, The Promise of Sleep