Home » Sleep Disorders » Nightmares
October 2020 |  Reviewed by:  Reeba Mathew, MD and Anne M. Morse, DO

What are nightmares?

Nightmares that occur frequently and keep you from getting restful sleep are considered a sleep disorder. Nightmare disorder is a parasomnia, a category of sleep disorders that involves unwanted events or experiences that occur while you are falling asleep or waking up or in your sleep.

If you have nightmare disorder, you may fear going to sleep or worry that each night you will have another nightmare. You may also feel anxious and scared when you wake up from a nightmare and be unable to go back to sleep. Sleep loss can cause you to have even more intense nightmares. As a result, you may experience daytime sleepiness.

Nightmares are usually coherent visual dreams that seem real and get more disturbing as they unfold and cause you to wake up. These most often happen towards the end of your sleep period. These dreams most often involve imminent physical danger. Nightmares may also focus on other distressing themes and provoke negative emotions such as:

  • Anxiety
  • Fear
  • Terror
  • Anger
  • Rage
  • Embarrassment
  • Disgust
  • Other negative feelings

In most instances after you wake up, you will be able to clearly remember the details of your nightmare. A disturbing dream that does not wake you up is not considered a nightmare. Instead, it is simply a bad dream. It is possible to have more than one nightmare, often with similar themes, during a night of sleep.

Nightmares tend to happen during REM sleep, the last stage in the sleep cycle. About 20% to 25% of your total sleep time is in REM sleep. The REM stage gets longer during each sleep cycle and your final period in REM may last up to an hour. As a result of this, nightmares are most likely to occur in the final third of the night. Nightmares that arise from trauma, such as in people with posttraumatic stress disorder (PTSD), may also occur in earlier sleep stages.