Nightmares — why we have them and what we can do

You wake with a jolt, heart pounding, a feeling of fear or unease still clinging to your body. It was only a dream — but it felt real. Nightmares are something most people experience from time to time, and although they can be deeply unpleasant, they’re usually completely harmless. But for some, nightmares become a persistent problem that steals sleep and affects daily life. This guide looks at what research says about why we have nightmares, what triggers them, and what you can actually do to bring them under control.

What exactly is a nightmare?

A nightmare is a vivid, distressing dream that usually occurs during REM sleep, particularly in the second half of the night. What sets a nightmare apart from an ordinary unpleasant dream is that you typically wake from it, and you remember the content afterward. The emotional reaction — fear, anxiety, sadness or disgust — is often strong enough to linger after you wake.

Nightmare content varies from person to person, but certain themes recur. Being chased is very common, as are dreams of falling, drowning, losing teeth, or finding yourself in a dangerous situation involving fire or a storm. Many also experience nightmares in which they’re naked in front of others, or unable to escape something threatening.

It’s worth distinguishing between ordinary nightmares and night terrors. Night terrors occur during deep NREM sleep, typically in the first part of the night. The person may scream, sit up in bed, or appear terrified, but rarely remembers anything afterward. Nightmares, by contrast, are dreams you remember, and they occur during lighter sleep.

Why do we have nightmares?

There’s no single cause of nightmares. Most often, it’s an interplay of several factors.

Stress and worry. The most common trigger for a nightmare is everyday stress. Periods of heavy pressure — whether from work, school, finances or relationships — can show up as unsettling dreams. The brain uses REM sleep to process emotional experience, and when emotional pressure is high, that process can take the shape of frightening dreams. Dreams of driving a car with no control, or being stuck in a dark room, often appear during stressful stretches.

Trauma. People who have experienced traumatic events — accidents, abuse, war, sudden loss — face a significantly higher risk of recurring nightmares. Trauma-related nightmares can reproduce the original event fairly precisely, or present it in a disguised form. In post-traumatic stress disorder (PTSD), recurring nightmares are one of the most prominent symptoms, and they can persist for years without treatment. See the article on PTSD and dreams for more.

Sleep deprivation and an irregular sleep pattern. Some people also experience sleep paralysis alongside disrupted sleep, which can accompany or trigger nightmares. Paradoxically, sleeping too little can increase the likelihood of nightmares. When you finally do get to sleep after a stretch of sleep deprivation, the body may compensate with longer, more intense REM periods — known as REM rebound. These intense periods are fertile ground for vivid, often unpleasant dreams. See the article on insomnia for more on this cycle.

Food, medication and substances. Certain medications, particularly some antidepressants and blood pressure drugs, can affect dream patterns. Alcohol suppresses REM sleep early in the night, leading to REM rebound toward morning — often bringing intense dreams or nightmares. Heavy food late in the evening may also play a role, though this varies from person to person.

Mental health conditions. Nightmares are more common in people with anxiety disorders, depression, and other mental health difficulties. It isn’t always clear what’s cause and what’s effect — poor sleep can worsen mental health, and poor mental health can worsen sleep. But the connection is well documented.

Image Rehearsal Therapy — a proven treatment

One of the most well-documented methods for treating recurring nightmares is Image Rehearsal Therapy (IRT). The technique is simple, can be done at home, and has shown good results in clinical studies.

The principle is that, during the day, you consciously rewrite the content of your nightmare. Here’s how:

Step 1: Write down the nightmare. Use your dream journal to write down the nightmare in detail. What happened? Where were you? What did you feel?

Step 2: Change the dream. Now write a new version of the dream — one where you have control, or where the outcome is positive. If you dreamed you were being chased by a threatening figure, the new version might have you turning around and confronting the figure, or the figure transforming into something harmless. It’s important that the new version feels meaningful and believable to you.

Step 3: Visualise the new dream. Spend ten to twenty minutes each day really picturing the new dream. Imagine it in detail — the images, the feelings, the outcome. The more vividly you can make the visualisation, the more effective it tends to be.

Studies have shown that IRT can reduce nightmare frequency by up to seventy percent, and that the effect often persists after treatment ends. The technique works for both everyday nightmares and more serious, trauma-related ones, though the latter are best handled together with a therapist.

Everyday changes that can help

Alongside IRT, there are a number of everyday steps that can reduce the likelihood of nightmares.

Establish good sleep routines. Go to bed and get up at roughly the same time every day. Avoid screens in the last hour before bed. Keep the bedroom dark, quiet and cool. Good sleep hygiene is the foundation for better dreams.

Reduce evening stress. Avoid intense conversations, the news, or stressful activities right before bed. Instead, try relaxation techniques like deep breathing, meditation or gentle yoga. Some people find that writing down worries in a notebook — a kind of “worry log” — helps the brain set thoughts aside before night.

Pay attention to what you eat and drink. Caffeine late in the day can affect sleep quality, and alcohol disrupts REM sleep even in moderate amounts. Heavy food right before bed can increase the chance of unsettled dreams.

Movement and physical activity. Regular exercise is one of the most effective ways to improve sleep quality. But avoid intense exercise in the last couple of hours before bed, since this can make it harder to fall asleep.

Talk about it. Sometimes sharing a nightmare with someone you trust can take the edge off it. Putting into words what frightened you can strip away some of its power. It isn’t therapy, but it’s a form of emotional processing that can help.

When to seek professional help

Most nightmares are temporary and don’t require treatment. But in some cases, it’s worth talking to a professional.

Consider contacting a doctor or psychologist if nightmares occur several times a week over an extended period, if they cause significant sleep loss that affects your daytime functioning, if they’re tied to a traumatic experience you haven’t processed, or if you feel anxious about going to sleep for fear of more nightmares.

A therapist can help you explore what’s behind the nightmares and offer structured treatment, whether that’s cognitive behavioural therapy for sleep problems, trauma treatment such as EMDR, or tailored IRT. Good help is available, and there’s no reason to suffer in silence.

Taking back the night

• Nightmares are common and usually harmless, but can become a problem if they’re frequent and persistent.
• The most common causes are stress, trauma, sleep deprivation and an irregular sleep pattern.
• Image Rehearsal Therapy (IRT) is a simple and effective technique for changing recurring nightmares.
• Good sleep hygiene, stress management and regular activity can reduce how often nightmares occur.
• Seek professional help if nightmares are significantly affecting sleep and daily functioning.

Nightmares can feel overwhelming in the moment, but they don’t have to run your nights. With the right tools and a little patience, you can take back control of your dreams.

Sources and further reading

• Ernest Hartmann, The Nature and Functions of Dreaming (2011) — the key work on nightmares as emotional processing.
• Antti Revonsuo, “The reinterpretation of dreams: An evolutionary hypothesis of the function of dreaming,” Behavioral and Brain Sciences 23(6), 2000 — the threat simulation theory: nightmares as the brain rehearsing danger.
• Matthew Walker, Why We Sleep (2017) — REM sleep and emotional regulation, and what happens when it’s disrupted.
• NHS — Sleep and tiredness