Nightmares in adults are often spontaneous. But they can also be caused by a variety of factors and underlying disorders. Some people have nightmares after having a late-night snack, which can increase metabolism and signal the brain to be more active. A number of medications also are known to contribute to nightmare frequency. Drugs that act on chemicals in the brain, such as antidepressants and narcotics, are often associated with nightmares. Non-psychological medications, including some blood pressure medications, can also cause nightmares in adults. Withdrawal from medications and substances, including alcohol and tranquilizers, may trigger nightmares. If you notice a difference in your nightmare frequency after a change in medication, talk with your doctor. Sleep deprivation may contribute to adult nightmares, which themselves often cause people to lose additional sleep. Though it's possible, it has not been confirmed whether this cycle could lead to nightmare disorder. There can be a number of psychological triggers that cause nightmares in adults. For example, anxiety and depression can cause adult nightmares. Post-traumatic stress disorder (PTSD) also commonly causes people to experience chronic, recurrent nightmares. Nightmares in adults can be caused by certain sleep disorders. These include sleep apnea and restless legs 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.