Brain On Nightmares: What Is Really Going On While You Sleep

  • Marisa Edmonds Master of Science - MS, Clinical Neuroscience, UCL, UK


Why do some dreams make us feel happy while others are scary or stressful? Do you know what happens when a bad dream wakes you up at night?

Dreams can be both fascinating and troubling. They come in different forms, from wonderful experiences to terrifying ones. However, some of these scary dreams are so intense that they wake us up, and we call them nightmares. It's normal to have a nightmare once in a while, but some people have them often, which can really affect their sleep and daily life.

People who experience nightmares this frequently tend to have a tough time with their sleep. They report feeling anxious about going to bed, waking up suddenly from sleep, struggling to fall back asleep, and having restless nights.

It's important to understand the distinctions between bad dreams, nightmares, and "nightmare disorder." This knowledge can be a starting point for figuring out why nightmares happen, finding the right treatments, and improving your sleep.1

Nightmares: The brain's mystery

Nightmares have a specific meaning in the world of sleep medicine that sets them apart from regular bad dreams. In everyday language, we often use the term "nightmare" to describe any scary or disturbing dream. However, in sleep medicine, nightmares have a more precise definition. They are dreams that not only feature unsettling content but also jolt us awake from our sleep.

  • Characteristics of nightmares: 

Nightmares are intense and vivid dreams that can be quite alarming. They often involve threatening, bizarre, or deeply unsettling scenarios. When you wake up from a nightmare, you tend to remember the dream very clearly, and many people feel upset or anxious afterwards.

  • Physical effects of nightmares:

As well as an emotional impact, nightmares can also have physical effects. You might notice changes in your heart rate or experience sweating after waking up from a nightmare. These physical symptoms  are part of the body's response to the distressing dream2

Nightmares vs. nightmare disorder

Let's explore the difference between ordinary nightmares and a more serious condition called nightmare disorder. We'll also look at how frequent nightmares can affect our lives.

While nightmares are something many of us experience, nightmare disorder is less common. But what exactly distinguishes one from the other?

Nightmare disorder is a type of parasomnia, which is sleep behaviours that aren't quite typical. Nightmare disorder occurs when nightmares happen frequently, causing distress, sleep disruptions, daytime problems, or even fear of going to sleep.

How common is nightmare disorder? It's relatively rare, affecting around 2% to 8% of people who struggle with nightmares that seriously impact their sleep.

Having the occasional nightmare doesn't mean you have nightmare disorder. This disorder is marked by recurring nightmares that significantly disrupt your daily life and well-being.3

  • Gender patterns and nightmares: 

Nightmares tend to surface in children between the ages of 3 and 6 but often decrease after age 10. However, some individuals continue to have nightmares as adults or throughout their lives. Interestingly, during the teenage and young adult years, people assigned female at birth seem to experience nightmares more frequently than people assigned male at birth. 

  • The severity of nightmare disorder: Nightmare disorder can vary in intensity, and it's categorised based on how often nightmares occur:
    • Mild: less than one nightmare per week, on average
    • Moderate: one or more nightmares per week, but not every night
    • Severe: nightmares happening every night

Understanding dreams and nightmares

The sleep stages and nightmares

To comprehend the link between nightmares and sleep stages, we need to first grasp what sleep stages are and how they connect to our dream experiences.

Our sleep is divided into different stages, one of which is called REM (Rapid Eye Movement) sleep. But what does REM sleep entail, and why is it significant?

REM sleep is a unique phase of our slumber. It's characterized by rapid eye movement (hence the name), irregular heartbeat, and increased breathing rate. Importantly, REM sleep is not continuous; it's broken into several episodes, making up roughly 20 per cent of our total sleep time. It's during these REM episodes that something called the "default network" in our brains becomes active, and this is when we're most likely to have vividly remembered dreams and nightmares.

Interestingly, as the night goes on, the REM stage of sleep gets longer with each sleep cycle. This means that your final round of REM sleep can last up to an hour, and it's during this time that nightmares are most likely to occur.3

Bad dreams, nightmares and night terrors

Bad dreams are those unsettling dreams that many of us have encountered. They can be distressing but don't usually wake us up from sleep. Nightmares, on the other hand, are not only disturbing but also wake us up during the night.

Night terrors are a more intense nighttime experience, often seen in children. They can involve kicking, screaming, and thrashing about, creating a more dramatic scene than a typical nightmare. But what really sets night terrors apart? One key distinction is that night terrors do not occur during REM sleep, which is when most nightmares happen.4

Why do we experience nightmares?

Exploring why we experience nightmares can be puzzling because there isn't a single agreed-upon explanation. In the world of sleep medicine and neuroscience, the concept of dreaming is still under debate. However, many experts believe that the causes of nightmares are linked to our emotional processing and memory consolidation.

One school of thought proposes that nightmares are a part of our emotional response to fear and trauma. They may serve as a way for our minds to process and cope with intense emotions and distressing experiences.

While these ideas provide valuable insights, it is important to note that more research is needed to explain why nightmares occur.4

Brain activity during nightmares

Fear processing in the brain 

Ever wondered why you jump in fright when something scary surprises you? Well, it's your brain at work and has some fascinating circuits dedicated to processing fear.

When something spooky or startling happens, your brain has a special set of circuits responsible for dealing with fear. These circuits are like internal alarm systems that kick in to get your body ready to respond.

Your brain isn't just about reacting to fear; it's also quite clever at learning from it. These fear-processing circuits help you figure out which situations are genuinely dangerous. So, if a spooky scare turns out to be a harmless Halloween costume, your brain will quickly catch on.

In serious situations, your brain's fear response becomes incredibly important for survival. Professor Bo Li from Cold Spring Harbor Laboratory highlights that the ability to feel fear helps us sense danger and is a driving force that motivates us to find ways to escape or defend ourselves.5

Triggers of nightmares

  • Stress or anxiety:

Life can get pretty stressful, right? Well, it turns out that everyday stressors like problems at home or work can sometimes be the trigger for nightmares. When stress and anxiety build up, they might find their way into your dreams.

  • Sleep deprivation:

Have you ever had a disrupted sleep schedule or not gotten enough rest? When you mess with your sleep patterns or don't get the sleep you need, it can increase the chances of having nightmares. Conditions like insomnia, which involve trouble sleeping, are often linked to more frequent nightmares.

  • Medications: 

Certain medications, although designed to help with various health issues, can have a surprising side effect: nightmares. These include medications for depression, anxiety, abnormal blood pressure, and Parkinson’s Disease. Quitting smoking can also trigger unsettling dreams. 

  • Substance misuse: 

Substance misuse, like excessive alcohol consumption, can lead to its own set of issues, including nightmares. When you withdraw from substances, your brain and body can react with nightmares.6

Nightmares and mental health

Nightmares are often linked to various psychiatric disorders. Additionally, not all nightmares are the same; some have known causes, while others remain a mystery. These include:

  • REM Behavior Disorder (RBD)
  • Narcolepsy
  • Sleep Apnea
  • Periodic Limb Movement Disorder (PLMD)
  • Post-Traumatic Stress Disorder (PTSD)
  • Generalised Anxiety Disorder
  • Social Anxiety Disorder
  • Depression

Idiopathic vs post-traumatic nightmares

Idiopathic nightmares are a type of disturbing dream, and the interesting thing is we don't always know why they happen. These nightmares don't seem to be connected to a specific traumatic event or PTSD.

Post-traumatic nightmares, on the other hand, are linked to traumatic experiences. They can occur shortly after the traumatic event during the acute stress response or continue as part of PTSD. It's important to note that nightmares are a common feature of PTSD, affecting as many as 90% of individuals with this condition.

What is particularly striking is that nightmares associated with trauma can persist for a very long time. In some cases, they may continue to haunt individuals for decades, up to 40–50 years after the initial traumatic event.6

Treatment of nightmares

After experiencing a traumatic event, many people try to forget and move forward. However, attempting to suppress thoughts and feelings can make nightmares related to the trauma more frequent. It's important to know when to seek help and what coping mechanisms are available.

Doctors, counsellors, and therapists are trained to assist with nightmares and other consequences of trauma. While there are medications that can help, experts often recommend starting with trauma-focused psychotherapy or counselling.

Therapeutic approaches for nightmares 

Several therapies can be effective in addressing trauma-related nightmares:

  • Desensitization and exposure therapies: These therapies involve controlled exposure to distressing thoughts and memories to reduce emotional reactions. Relaxation techniques are taught to help manage emotions during and after exposure.
  • Image rehearsal therapy (IRT): IRT includes writing down a nightmare and transforming it into a story with a positive resolution. This new story can be read before bedtime, potentially reducing the frequency of nightmares.
  • Lucid dreaming: Lucid dreaming involves becoming aware that you are dreaming while you're still in the dream. This awareness can empower you to change or resolve events within the dream, potentially reducing the distress caused by nightmares.3

How to cope with nightmares 

In addition to seeking professional support, consider these strategies to support healthy sleep hygiene:

  • Recognize normal symptoms: After a traumatic experience, it is common to have trouble sleeping. Understand that these symptoms are normal as your body processes the event.
  • Maintain routine: Stick to your regular sleep schedule, even when dealing with trauma. Consistency in your daily activities can promote better sleep.
  • Relax before bed: Instead of pressuring yourself to fall asleep, focus on calming your mind and body before bedtime. Turn off electronic devices and try relaxation techniques to ease into sleep.
  • Don't stay in bed if You can't sleep: If you find yourself lying awake for more than 20 minutes, get out of bed and engage in relaxing activities like reading or listening to soothing music to avoid associating the bed with sleeplessness.3


  • Nightmares are intense, anxiety-inducing dreams that wake you up during the night, in contrast to regular bad dreams.
  • Nightmares mainly occur during the final REM cycle, (which can last up to an hour.
  • Although not fully understood, experts believe nightmares might aid the processing of emotions and memories, especially related to fear and trauma.  Special circuits in the brain process fear, crucial for sensing danger and survival, as well as learning from experiences.
  • Nightmares can be triggered by stress, sleep disruption, medications, and substance misuse, affecting sleep quality.
  • Nightmares are linked to psychiatric conditions like PTSD, anxiety, and depression, either idiopathically or due to trauma.
  • Seek professional help, such as trauma-focused therapy for trauma-related nightmares. Therapies like desensitisation, image rehearsal, and lucid dreaming can assist. Maintaining routines and relaxation techniques will support better sleep hygiene


  1. Nightmares: Symptoms, Causes, & Treatment. Sleep Foundation, (2020, Accessed 29 September 2023).
  2. Nightmare Disorder: What It Is, Symptoms & Treatment. Cleveland Clinic, (Accessed 29 September 2023).
  3. Nightmare disorder - Symptoms and causes. Mayo Clinic, (Accessed 29 September 2023).
  4. Hasler B, Germain A. Correlates and Treatments of Nightmares in Adults. Sleep Med Clin 2009; 4: 507–517.
  5. Paul F, Schredl M, Alpers GW. Nightmares affect the experience of sleep quality but not sleep architecture: an ambulatory polysomnographic study. Borderline Personal Disord Emot Dysregul 2015; 2: 3.
  6. Michalowski J. How does the brain process fear? Cold Spring Harbor Laboratory, (2020, Accessed 29 September 2023).
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Marina Ramzy Mourid

Bachelor of Medicine, Bachelor of Surgery - MBBS, Alexandria University

Marina Ramzy Mourid, a diligent medical student at Alexandria University in Egypt, has a strong passion for neurology and a keen interest in research. With a love for science communication, Marina excels not only in her studies but also as a prolific medical writer and author. Her track record speaks volumes, having clinched numerous competitions in article writing over the years.

Her primary goal is to empower people through the dissemination of medical knowledge.

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With her academic prowess and commitment to making medicine understandable, Marina Ramzy Mourid is poised to make a lasting impact in the field of healthcare and medical education. presents all health information in line with our terms and conditions. It is essential to understand that the medical information available on our platform is not intended to substitute the relationship between a patient and their physician or doctor, as well as any medical guidance they offer. Always consult with a healthcare professional before making any decisions based on the information found on our website.
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