Stage Four Sleep is the period when Sleep Terror Disorder (also known as Night Terrors or pavor nocturnes) occurs.
The answer to what causes night terrors varies between sleepers and can vary with their age and lifestyle. Night terrors are known by several names: Sleep terrors, night terrors, sleep terror disorder and pavor nocturnus.
Unlike a sleep disorder like snoring, it is very difficult to pinpoint the exact cause of night terrors.
This leads researchers to believe that night terrors might be caused by a chemical reaction in the body that causes a "misfire" in the brain.
What causes night terrors can vary from the stress felt by a three year old during a family divorce to a medication-induced night terror in an adult.