Why Do Nightmares Happen?
Nightmares happen when the brain processes stress, fear, and emotional memories during REM sleep. They are often linked to nervous system activation, trauma, anxiety, and unresolved stress. They are not random, and they are not a sign that something is wrong with you.
Nightmares are not random, or a sign that something is broken in you. They’re not punishment or moral judgment.
They are sleep disturbances that are rooted in brain function, emotional processing, and how your nervous system reacts to threats and stress. They are also informed by our activities and lives, such as the media we consume.
Jump to: How Common Are Nightmares? · REM Sleep · The Feedback Loop · Trauma · Fear Conditioning · When to Seek Help · Not a Failure
How Common Are Nightmares?
Nightmares are far more common than most people think.
Research indicates that between 2–6% of adults experience nightmares weekly, and 8–29% report them monthly (Hasler & Germain, 2009). Nightmare disorder—when nightmares are distressing enough to disrupt daily life—affects approximately 4% of the adult population (Hasler & Germain, 2009).
Looking specifically at trauma, particularly post-traumatic stress disorder (PTSD), the prevalence skyrockets. In clinical populations, up to 90% of people with PTSD report disturbing dreams (Hasler & Germain, 2009). In broader community samples, 52–71% of people with PTSD report recurrent nightmares (Wittmann et al., 2007).
There is also a genetic component. Research suggests that roughly 37% of the variation in adult nightmare frequency and about 45% of the variation in childhood nightmares can be attributed to genetics (Hasler & Germain, 2009). Some people are simply more biologically prone to nightmares than others—and that is not a character flaw.
Nightmares are not rare, and they’re not imaginary. They are part of how the brain and nervous system respond to emotional load, threat learning, and sleep processes.
Nervous System and REM Sleep
Nightmares most often occur during REM (rapid eye movement) sleep, the stage when dreaming is most vivid. In REM:
- Emotional centers (like the amygdala) are highly active
- The parts of the brain responsible for logic and regulation are quieter
- The body is temporarily paralyzed
- Emotional processing continues without full waking oversight
In people with PTSD or chronic stress, the amygdala can become overreactive while the brain’s ability to regulate that response is weakened (Germain & Zadra, 2009). REM sleep naturally activates these emotional areas—which means in a stressed or traumatized brain, sleep itself can become fertile ground for fear reactivation.
It’s also worth noting that nightmares are not exclusively a REM phenomenon. Research has found that 57% of trauma-related nightmares occur during REM sleep, but 27% occur during Stage 2 sleep and 10% during Stage 1 (Wittmann et al., 2007). This suggests nightmares reflect broader fear activation across sleep stages, not simply a REM malfunction.
Stress, Anxiety, and the Nightmare Feedback Loop
Even those without PTSD can have disruptive nightmares.
Chronic stress alone can contribute to nightmare frequency. Emotions that are not fully processed during the day can keep the body’s alarm system activated. The brain may carry that tension into sleep.
This can create a vicious cycle: nightmares disrupt sleep, disrupted sleep increases daytime sensitivity and emotional reactivity, heightened reactivity worsens stress, and worsened stress produces more nightmares (Rothbaum & Mellman, 2001).
Research supports this directly. Nightmares have been found to independently contribute to PTSD severity, alcohol use, and reduced quality of life—suggesting their impact extends well beyond the nighttime hours (Germain & Zadra, 2009).
This is why people who report nightmares often also report difficulties in relationships, emotional regulation, and daily functioning.
Trauma and Hyperarousal
In people affected by trauma—especially those with PTSD—the nervous system becomes hypersensitive. Instead of activation returning to baseline after a perceived threat subsides, it stays elevated. This heightened state is linked with increased nightmare frequency and intensity.
Nightmares may initially serve an emotional processing function—the brain’s attempt to work through overwhelming experiences during sleep. But when they persist, research suggests they can flip into a sensitization loop, reinforcing fear activation rather than resolving it (Germain & Zadra, 2009).
At that point, the nightmares are no longer trying to heal. They may be maintaining the problem.
Expectation and Fear Conditioning
An under-discussed but critical factor is anticipatory anxiety. When someone begins to expect nightmares, their nervous system often starts preparing for threat before sleep. This creates:
- Pre-sleep tension
- Greater nervous system activation
- Difficulty falling asleep
- Higher likelihood of emotionally intense dreams or nightmares
Researchers describe recurring nightmares as learned “scripts”—storylines the brain has rehearsed so many times that even a subtle emotional cue during sleep can trigger the whole sequence (Spoormaker et al., 2006). Once the script is established, it can replay with very little provocation.
Over time, sleep becomes associated with danger rather than rest. This expectation reinforces a self-perpetuating nightmare cycle. The good news is that if nightmares can be learned, they can also be unlearned. Structured approaches like imagery rehearsal therapy (IRT) work by modifying the script and breaking the cycle (Krakow et al., 2001).
If you’d like structured guidance for building a better nightmare response—including exactly what to do when you wake from a nightmare—I’ve created a printable bedside instruction sheet for exactly that moment.
I’ve also included a five minute audio recording in case you’d rather listen on your phone when you need to.
When Nightmares Deserve Attention
Occasional nightmares are common and usually not a cause for concern.
But frequent nightmares should not be dismissed. Research has found that nightmares are associated with elevated suicide risk—even after accounting for depression and other psychiatric conditions. Occasional nightmares were linked to 57% higher risk, and frequent nightmares to 105% higher risk. Nightmares were the only sleep-related factor that remained significant after controlling for other mental health conditions (Hasler & Germain, 2009).
Additional research found that 62% of nightmare sufferers reported suicidal behaviors compared to 20% of non-sufferers—and this held true independent of both depression and insomnia (Albanese et al., 2022).
This does not mean nightmares cause suicidal thoughts. It means they are a meaningful signal that deserves clinical attention rather than dismissal.
Consider seeking professional support if nightmares are occurring weekly or more, following trauma, replaying the same storyline, causing you to avoid sleep, or accompanied by persistent feelings of hopelessness.
If you are experiencing thoughts of self-harm, please reach out for support. In the United States, you can call or text 988, the Suicide & Crisis Lifeline. If you are outside the United States, contact local emergency services or a crisis hotline in your region.
Nightmares as a Symptom, Not a Failure
Nightmares are often symptomatic of underlying patterns such as:
- Overloaded emotions
- Incomplete stress processing
- Hypervigilance of the nervous system
- Fragmented sleep
- Memory consolidation under stress
It’s important to realize that having nightmares does not make you defective.
You are likely experiencing a sleep manifestation of deeper processes in the brain and nervous system.
But there’s good news. Since nightmares are tied to measurable systems—nervous system activation, REM activity, emotional memory—they can be changed. They are not fate.
A review of nine controlled studies found that nightmare-focused treatments produced large to very large improvements in nightmare frequency (Lancee et al., 2008). Imagery rehearsal therapy holds the highest recommendation level from the American Academy of Sleep Medicine as the treatment of choice for nightmare disorder (Albanese et al., 2022).
References
- Albanese, M., Liotti, M., Cornacchia, L., & Mancini, F. (2022). Nightmare rescripting: Using imagery techniques to treat sleep disturbances in post-traumatic stress disorder. Frontiers in Psychiatry, 13, 866144.
- Germain, A., & Zadra, A. (2009). Dreams and nightmares in PTSD. In L. R. Squire (Ed.), Encyclopedia of Neuroscience (Vol. 3, pp. 655–661). Oxford: Academic Press/Elsevier.
- Hasler, B. P., & Germain, A. (2009). Correlates and treatments of nightmares in adults. Sleep Medicine Clinics, 4(4), 507–517.
- Krakow, B., Johnston, L., Melendrez, D., Hollifield, M., Warner, T. D., Chavez-Kennedy, D., & Herlan, M. J. (2001). An open-label trial of evidence-based cognitive behavior therapy for nightmares and insomnia in crime victims with PTSD. American Journal of Psychiatry, 158(12), 2043–2047.
- Lancee, J., Spoormaker, V. I., Krakow, B., & van den Bout, J. (2008). A systematic review of cognitive-behavioral treatment for nightmares. Journal of Clinical Sleep Medicine, 4(5), 475–480.
- Rothbaum, B. O., & Mellman, T. A. (2001). Dreams and exposure therapy in PTSD. Journal of Traumatic Stress, 14(3), 481–490.
- Spoormaker, V. I., Schredl, M., & van den Bout, J. (2006). Nightmares: From anxiety symptom to sleep disorder. Sleep Medicine Reviews, 10(1), 19–31.
- Wittmann, L., Schredl, M., & Kramer, M. (2007). Dreaming in posttraumatic stress disorder: A critical review. Psychotherapy and Psychosomatics, 76(1), 25–39.