|A nightmare is a dream occurring during rapid eye movement (REM) sleep that results in feelings of strong fear, distress or extreme anxiety. Nightmare stands to occur in the latter part of the night and oftentimes awakens the sleeper, who is likely to recall the content of the dream. Nightmares may seem real, often becoming more disturbing as the dream unfolds. But nightmares usually are nothing to worry about. Nightmares may become a problem if you have them frequently and they cause you to fear going to sleep or keep you from sleeping well. Most nightmares may be a normal reaction to stress, and some clinicians believe they aid people in working through traumatic events. Frequent occurrence of nightmares becomes a disorder when it impairs social, occupational and other important areas of functioning. At this point, it may be referred to as Nightmare Disorder (formerly Dream Anxiety Disorder) or "repeated nightmares." The subjects of nightmares vary from person to person. There are, though, some common nightmares that many people experience. For example, a lot of adults have nightmares about not being able to run fast enough to escape danger or about falling from a great height. If you've gone through a traumatic event, such as an attack or accident, you may have recurrent nightmares about your horrifying experience. Nightmares in adults can be caused by certain sleep disorders. These include sleep apnea and restless leg syndrome. If no other cause can be determined, chronic nightmares may be a distinct sleep disorder. People who have relatives with nightmare disorder may be more likely to have the condition themselves.