Nightmares: Why They Happen and How to Reduce Them

Sources

  1. Walker, M. P. & van der Helm, E. (2009). "Overnight therapy? The role of sleep in emotional brain processing." Psychological Bulletin, 135(5), 731-748. PubMed 19702380.
  2. Peever, J. & Fuller, P. M. (2017). "The biology of REM sleep." Current Biology, 27(22), R1237-R1248. PubMed 29161567.
  3. Simor, P. et al. (2012). "Nightmares and bad dreams in patients with borderline personality disorder." Psychiatry Research, 199(1), 34-40. PubMed 22503363.
Quick Answer: Nightmares happen during REM sleep and are most commonly triggered by psychological stress, PTSD, certain medications, alcohol, and sleep deprivation. Occasional nightmares are normal. When nightmares are frequent, distressing, and disrupting sleep, nightmare disorder is the clinical description, and imagery rehearsal therapy (IRT) is the most evidence-supported treatment. For medication-related nightmares, speak with the prescribing physician.
Table of Contents

8 min read

Why Nightmares Happen

Nightmares are vivid, disturbing dreams that typically occur during REM (rapid eye movement) sleep, most commonly in the latter half of the night when REM periods are longest. They differ from night terrors, which occur during non-REM deep sleep and are not experienced as narratives, someone in a night terror episode is not dreaming in the conventional sense.

During REM sleep, the brain is highly active, processing emotional memories, consolidating experiences, and running through scenarios including threatening ones. This emotional processing function of REM sleep is likely why distressing experiences and emotional stress translate into nightmare content. The brain is working through difficult material.

REM Sleep and Emotional Processing: Research from Matthew Walker and others suggests REM sleep serves a specific function in emotional memory processing, replaying emotionally significant experiences in a neurochemical environment that strips the emotional charge from the memory while preserving the factual content. Nightmares may represent this process working on difficult or threatening material. PTSD disrupts this process: the emotional charge doesn't discharge normally, and the threatening memory gets replayed with full intensity rather than processed.

Common Nightmare Triggers in Adults

  • Psychological stress and anxiety: The most common cause of increased nightmare frequency in adults without a trauma history. Work pressure, relationship difficulties, and life transitions commonly correlate with nightmare periods.
  • PTSD and trauma: Trauma-related nightmares are a core symptom of PTSD. The nightmares often directly replay the traumatic event or variations of it.
  • Medications: Several medication classes are associated with vivid dreams and nightmares: antidepressants (especially SSRIs and SNRIs), beta-blockers (commonly prescribed for blood pressure), melatonin (high doses), and medications being withdrawn from (the withdrawal of REM-suppressing substances causes REM rebound with intense dreaming).
  • Alcohol: Alcohol suppresses REM sleep in the first part of the night, then causes REM rebound in the second half as alcohol is metabolized, producing vivid, often disturbing dreams. Regular drinkers who quit often experience intense dream periods as REM rebounds.
  • Sleep deprivation: Extended wakefulness followed by sleep produces REM rebound, longer and more intense REM periods. Vivid dreams and nightmares are common after sleep deprivation.
  • Fever and illness: Elevated body temperature and immune system activity are associated with vivid and disturbing dream content.

Nightmare Disorder vs Occasional Bad Dreams

Occasional nightmares are normal and do not require treatment. Most adults experience nightmares a few times per year in response to stress, illness, or alcohol.

Nightmare disorder is a clinical condition defined by:

  • Repeated episodes of vivid, disturbing dreams, typically in the second half of sleep
  • The person wakes up and is immediately alert and oriented (different from night terrors, where the person is confused and disoriented)
  • The nightmares cause clinically significant distress or impair daytime functioning (affecting mood, sleep avoidance, fear of sleeping)
  • Frequency: typically multiple times per week

Evidence-Based Treatments for Nightmares

Imagery Rehearsal Therapy (IRT)

The most evidence-supported non-pharmacological treatment for chronic nightmares. The method:

  1. Write out the recurring nightmare in as much detail as you recall
  2. Rewrite the nightmare with a different, non-threatening ending of your choosing, any alternative that isn't frightening
  3. Rehearse the new version of the dream story in waking imagination, 10-20 minutes daily

Multiple clinical trials have shown IRT significantly reduces nightmare frequency and intensity, particularly for PTSD-related nightmares. The mechanism: deliberate waking rehearsal of an alternative narrative competes with the established nightmare pattern and can reduce or eliminate it over 2-4 weeks.

Sleep Hygiene Improvements

Addressing the modifiable triggers: eliminating alcohol especially near bedtime, treating sleep deprivation, managing stress with daytime techniques (exercise, therapy, meditation), and addressing medication contributions with the prescriber.

Pharmacological Treatment

Prazosin (an alpha-blocker originally for blood pressure) has evidence for reducing PTSD-related nightmares and is sometimes prescribed off-label. Pharmacological treatment is typically used when psychological approaches haven't been sufficient and should be managed by a physician.

Lucid Dreaming Techniques

Some individuals learn to recognize they are dreaming during a nightmare (lucid dreaming) and change the dream narrative in real time. This requires practice but can be effective for people who experience recurring nightmares with recognizable elements.

Frequently Asked Questions

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What causes nightmares in adults?

The most common causes are psychological stress, PTSD, certain medications (antidepressants, beta-blockers), alcohol (causes REM rebound), sleep deprivation, and illness. Nightmares related to a medication that was recently started or recently stopped should be discussed with the prescribing physician.

What is nightmare disorder?

Nightmare disorder is a clinical condition where nightmares are frequent (multiple per week), distressing, and impair sleep or daytime functioning. It's distinct from occasional bad dreams. Nightmare disorder, particularly when PTSD-related, is treated with imagery rehearsal therapy (IRT) and, in some cases, pharmacological support.

What is imagery rehearsal therapy for nightmares?

IRT involves writing down a recurring nightmare, rewriting it with a different non-threatening ending, then rehearsing the new version mentally for 10-20 minutes daily. Over 2-4 weeks, the rehearsed alternative often displaces the nightmare pattern. It's the most evidence-supported treatment for chronic nightmares with multiple clinical trials demonstrating significant reductions in nightmare frequency.

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Written by , Content Specialist at Mattress Miracle. Topical expertise sourced from Brad Grose (founder, 1997), Talia Grose (sleep specialist), and Dorothy Balicki (40+ years industry).

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