Causes

Nightmare disorder is referred to by doctors as a parasomnia — a type of sleep disorder that involves undesirable experiences that occur while you're falling asleep, during sleep or when you're waking up. Nightmares usually occur during the stage of sleep known as rapid eye movement (REM) sleep. The exact cause of nightmares is not known.

Nightmares can be triggered by many factors, including:

• Stress or anxiety. Sometimes the ordinary stresses of daily life, such as a problem at home or school, trigger nightmares. A major change, such as a move or the death of a loved one, can have the same effect. Experiencing anxiety is associated with a greater risk of nightmares.
• Trauma. Nightmares are common after an accident, injury, physical or sexual abuse, or other traumatic event. Nightmares are common in people who have post-traumatic stress disorder (PTSD).
• Sleep deprivation. Changes in your schedule that cause irregular sleeping and waking times or that interrupt or reduce the amount of sleep you get can increase your risk of having nightmares. Insomnia is associated with an increased risk of nightmares.
• Medications. Some drugs — including certain antidepressants, blood pressure medications, beta blockers, and drugs used to treat Parkinson's disease or to help stop smoking — can trigger nightmares.
• Substance misuse. Alcohol and recreational drug use or withdrawal can trigger nightmares.
• Other disorders. Depression and other mental health disorders may be linked to nightmares. Nightmares can happen along with some medical conditions, such as heart disease or cancer. Having other sleep disorders that interfere with adequate sleep can be associated with having nightmares.
• Scary books and movies. For some people, reading scary books or watching frightening movies, especially before bed, can be associated with nightmares.