A night terror, also known as a sleep terror, is a sleep disorder that causes extreme terror and a temporary inability to regain full consciousness. The person having the night terror wakes up suddenly, usually gasping, moaning, or screaming while waking. It is often impossible to wake up the person fully because they are so concentrated on waking, and after the terror the subject normally settles back to sleep without waking. A night terror can rarely be recalled by the subject. They typically occur during non-rapid eye movement sleep.