Nightmares can be associated with another sleep disorder. Many other factors can trigger nightmares, including:

  • Stress. 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.
  • Trauma. Nightmares are common after an accident, injury or other traumatic event. Nightmares are prominent in post-traumatic stress disorder (PTSD).
  • Scary books and movies. Reading scary books or watching scary movies, especially before bed, can cause nightmares.
  • Bedtime snacks. For some, eating right before bed — and the resulting boost in metabolism and brain activity — leads to nightmares.
  • Illness. Sometimes being sick triggers nightmares, especially if the illness is accompanied by a fever.
  • Medications. Some drugs — including certain antidepressants, narcotics, barbiturates, beta blockers and drugs used to treat Parkinson's disease — can trigger nightmares.
  • Substance abuse. Alcohol and illegal drugs can trigger nightmares.

Most nightmares occur during rapid eye movement (REM) sleep. You normally go through four to six sleep cycles a night, cycling through the sleep stages in about 90 minutes. Your REM stage lengthens with each cycle, from several seconds in the first cycle to up to an hour in the last. You're more likely to have a nightmare in the last third of your night.

Aug. 12, 2011