National Sleep Foundation

Chapter 6: Parasomnias

Nightmare and Sleep-Related Hallucinations

Nightmares are disturbing mental experiences that generally occur during Rapid Eye Movement (REM) sleep (during the later portion of the night) and often result in the person waking up1.  Having an occasional nightmare is normal. A nightmare disorder is diagnosed only when a person’s nightmares become more frequent and significantly affect his or her daytime functioning and mood.
Nightmares are associated with limited autonomic activation and people usually remember them when they wake up. “Sleep terrors,” on the other hand, are extreme nightmares that occur during non-REM sleep. The person usually does not remember the content after he or she wakes up2.

Sleep-related hallucinations occur during sleep onset (hypnagogic) or upon awakening from sleep (hypnopompic); these hallucinations can seem very real and can be very frightening3.   The hallucinations consist predominantly of complex visual images, although auditory, tactile, or kinetic events may occur. They can remain present for many minutes, but will usually disappear, often with an increase in ambient light4.

Beyond nightmares, dreaming disturbances can also occur as comorbidities associated with other medical conditions, such as migraines, Post-Traumatic Stress Disorder (PTSD), epilepsy, or withdrawal from certain medications5.  
The International Classification of Sleep Disorders (ICSD) lists Nightmare Disorder as a REM-Related Parasomnia, and sleep-related hallucinations under “Other Parasomnias.”6

References

  1. Nielson T, Zadra A, “idiopathic Nightmares and Dream Disturbances Associated with Sleep-Wake Transitions,” in Kryger M, Roth T, Dement W (ed.), Principles and Practice of Sleep Medicine (5th Edition), St. Louis: Elsevier Saunders, 2011, pages 1106-1115.
  2. National Sleep Foundation, “Sleep Disorders: Nightmares and Sleep,” Arlington, VA: NSF, no date. Available online at: https://sleepfoundation.org/sleep-disorders-problems/abnormal-sleep-behaviors/nightmares-and-sleep.
  3. Nielson T, Zadra A, “Idiopathic Nightmares and Dream Disturbances Associated with Sleep-Wake Transitions,” in Kryger M, Roth T, Dement W (ed.), Principles and Practice of Sleep Medicine (5th Edition), St. Louis: Elsevier Saunders, 2011, pages 1106-1115.
  4. Nielson T, “Disturbed Dreaming as a Factor in Medical Conditions,” in Kryger M, Roth T, Dement W (ed.), Principles and Practice of Sleep Medicine (5th Edition), St. Louis: Elsevier Saunders, 2011, pages 1116-1127.
  5. Silber MH, Hansen MR, Girish M. Complex nocturnal visual hallucinations. Sleep Med. 2005;6:363-366.
  6. American Academy of Sleep Medicine, International Classification of Sleep Disorders (Third Edition), Darien, IL: American Academy of Sleep Medicine, 2014.