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.

Interestingly, the data shows they are far more common than most people think.

Research indicates that between 4–8% of adults have a “current problem” with ongoing nightmares. About 3% report nightmares weekly, and roughly 10% report them monthly.¹ Another study found that about 5.3% of adults have a current nightmare problem using clinical criteria.¹ Nightmare disorder—when nightmares are distressing and disruptive—affects approximately 4% of the adult population.¹

Looking specifically at trauma, particularly post-traumatic stress disorder (PTSD), the prevalence skyrockets. Research shows that as many as 90% of trauma-exposed individuals who develop PTSD report disturbing dreams.² Community estimates of PTSD prevalence range from 1–10%, meaning a significant number of people may be living with both trauma and disrupted sleep states.²

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, REM sleep processes, and trauma.

Nervous System and REM Sleep

Nightmares usually occur during REM (rapid eye movement) sleep, the stage when dreaming is most vivid. In REM:

Emotional centers (like the amygdala) are highly active
Logical/memory centers are less dominant
The body is temporarily paralyzed
Emotional processing continues without full waking regulation

For people under chronic stress or trauma, REM sleep can become a time when unresolved or highly charged experiences emerge with maximum emotional intensity.

Statistically, nightmares occur in a meaningful subset of people because REM sleep can reflect emotional processing and threat signaling rather than random imagery.

Stress, Anxiety, and Memory Processing

Even those without full PTSD can have disruptive nightmares.

In fact, chronic stress alone can contribute to nightmare frequency.

Life is overwhelming, and emotions that are not fully processed during the day can cause your body’s alarm system to “stay on.” The brain may carry that tension into sleep. Sadly, nightmares can then become a kind of feedback loop:

Stress leads to sleep disruption, which increases nightmares, which increases stress.

This is why people who report nightmares often also report difficulties in relationships, emotional regulation, and daily functioning.

Trauma and Hyperarousal

In individuals that are trauma-affected—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 stress response is linked with increased nightmare frequency and intensity.

This reinforces the idea that nightmares are part of how the brain responds to ongoing emotional load and threat recall.

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

Over time, sleep becomes associated with danger rather than rest. This expectation reinforces a perpetual nightmare cycle.

Nightmares as a Symptom, Not a Failure

Finally, nightmares are often symptomatic of underlying patterns such as:

Overloaded emotions
Incomplete stress processing
Hypervigilance of the nervous system
Fragmented sleep
Memory consolidation mechanisms

It’s important to realize that having nightmares does not make you defective.

You are likely experiencing a sleep manifestation of deeper neurophysiological and psychological processes.

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.

Structured methods and techniques can be very helpful in reducing intensity, interrupting repetition, and building control around dream responses.

Sources

Spoormaker, V. I., & Schredl, M. (2003). Nightmares: From anxiety symptom to sleep disorder. Sleep Medicine Reviews, 7(2), 187–205.
Germain, A., & Zadra, A. (2009). Dreams and nightmares in PTSD. Clinical Psychology Review, 29(6), 558–570.