Nightmares and Night Terrors Did you know that nightmares are different then night terrors? They occur in different stages of sleep. Nightmares occur in REM (rapid eye movement) sleep/ Night terrors occur during NREM sleep. A nightmare is an unsettling dream which usually causes partial awakening. A person can feel many emotions. A night terror is not really a dream, but a sudden reaction of fear that happens when you change the sleep phases from one to another. Night terrors mostly occur about two or three hours after a child falls asleep. When sleep transitions from the deepest stage of non REM sleep to a lighter stage of REM sleep, a stage where dreams usually happen. During a night terror, a child might seem to be very active, such as screaming, sweating, and sitting straight up in bed. After a little while they should calm down. In nightmares you can sometimes remember the dreams you dream, but in night terrors kids will not have any memories of it because they were in a deep sleep and there are no mental images to remember. What causes a night terror? A night terror is caused by the Central Nervous System. This may happen because the CNS (which regulates sleep and brain activity) is still growing. About 80% of people who have night terrors have a family member who also had night terrors or sleepwalking problems.