Unpleasant, frightening, and waking dreams are called nightmares. They can cause undesirable emotional reactions, such as fear or anxiety. Nightmares most often occur during the REM phase of sleep. Nightmares are a separate phenomenon from sleep terrors but are often confused. Although they can occur at any age, they are more common in children and adolescents. The exact etiology is unknown; however, they can be associated with fear and emotional traumas. On the other hand, when nightmares become more frequent, they can disrupt sleep quality and negatively affect daily life, indicative of a nightmare sleep disorder.