Sleep Science

Why do we dream and have nightmares?

An image of Abi Hayward
12 Jul 202210.5 min read

Why do we dream? And why do we have nightmares? These are two questions you’ve probably asked yourself after waking up from a weird dream or creepy nightmare.

Dreams themselves happen during the rapid eye movement (REM) stage of sleep. This is because REM sleep triggers different parts of the brain to create electrical impulses, which can cause random images and thoughts to occur. These flashes of thoughts, feelings and images can influence or appear in your dream.

Although we know how we dream, scientists do not have a solid answer for why we dream. However, there are a few different theories that could explain why we dream. They could help us:

  • Process emotions
  • Improve our long-term memory
  • Express wishes and desires
  • Be more creative

If you’re interested in learning more about what exactly dreams are, the science of dreams and how you can remember your dreams, read on!

What are dreams?

Dream definition: 

‘a series of thoughts, images, and sensations occurring in a person's mind during sleep.’

Oxford Languages

Dreams, essentially, are hallucinations and images that our brains create for us while we are asleep. They are strange and unique due to the way our ‘sleeping’ brains process time, reality and memories very differently than our ‘waking’ brains.

People experience the most realistic and vivid dreams during REM (rapid eye movement) sleep, which is when you sleep the lightest. REM sleep cycles every 90 minutes to 2 hours.

You can also dream in NREM (non-rapid eye movement sleep), but these dreams are more likely to be more understandable. Scientists believe this is because your brain is more likely to be connected to your thoughts and feelings in this stage.

How long do dreams last?

Even if a dream feels like it lasts for hours, it’s probably only taking place over twenty minutes at most. We only dream for up to two hours each night. This is because we can only dream during certain stages of the 5-step sleep cycle.

Alarm clock next to sleeping woman

Why do we dream?

How we dream is down to a collection of electrical impulses which are triggered by the hippocampus and amygdala in the process of REM sleep. But there are many different theories on why we dream, ranging from scientific to emotional.

Dreams aid long-term memory

One of the most popular theories for the purpose of dreams is that dreaming helps your brain to make long-term connections to remember important information. This is because your brain will preserve some memory connections over others. That is why you may find it easier to remember certain things when you wake up in the morning.

Dreams are a response to fight or flight instincts

Some scientists believe that dreams are a way that your brain reacts to the amygdala section of your brain. The amygdala is partially responsible for your fight or flight instinct and is most active while you’re asleep. This could mean that dreams are your brain’s automatic reaction to this instinctive part of the brain being activated. 

Fortunately, REM sleep relaxes your muscles, which prevents you from acting out these dreams in your sleep.

Dreams can act as practice for potential dangers

Have you ever had a dream where you’re being chased, falling or are in a life-threatening situation? Well, it is believed by some that your brain can simulate these dangers while you are asleep to prepare your body in case you face these threats in the future.

Dreams help to reset your brain at the end of a day

It is also suggested that dreams help to cleanse your mind after a long day, allowing your brain to distinguish between important information and information that can be forgotten. Essentially, the idea behind this theory is that the brain is clearing itself out to make room for fresh new thoughts when you wake up.

Woman waking up stretching

Dreams caused by your sleeping environment

A different theory about dreams is that they are caused by external factors while you sleep. For example, dreams may be your brain trying to interpret noises and differences in light that occur around you as you slumber.

Dreams help to express your wishes and desires

Famous neurologist Sigmund Freud believed that dreams are a subconscious way of expressing our deepest desires. They are wishes and goals in life that we would otherwise not acknowledge while conscious. He did extensive research into the psychology of dreams, which he recorded in his book 'The Interpretation of Dreams'.

Dreams help us to process our emotions

Some people believe that dreams may help us subconsciously process our feelings and emotions. The idea is that this can help to clear the mind and allow us to destress while we sleep so we wake up feeling more refreshed.

Dreams help to improve creativity

As your brain is allowed to think freely while you sleep, many people believe that dreams help us become more creative during our waking life. Dreams may also aid learning by allowing us to make new connections in our unconscious minds. In our other post, we talk about some of the best discoveries that came from dreams, why not check it out?

Woman painting in her bedroom

Dreams keep the brain active

More simply, some scientists believe that dreams are just a way of keeping your brain working and active while you’re asleep. 

Dreams are just dreams!

Alternatively, a large group of scientists think that dreams are just what they are - dreams. They believe that they’re just a result of your human-brain sleeping and that they hold no greater meaning.

These are just some of the theories and ideas behind the science of dreams!

Things that can influence dreams and nightmares

Did you know that certain aspects of your life may influence your dreams and nightmares? This may affect how much you dream, the types of dreams you have and how much time you spend in the 5 different stages of the sleep cycle.

Health or medical conditions

Certain health conditions can affect how you sleep, which can impact your dreams. For example: 

  • Sleep deprivation - When you manage to sleep after sleep deprivation, it can induce more REM sleep. REM sleep is often when we have our most vivid dreams, so when you sleep after experiencing sleep deprivation, you may find that your dreams are more surreal for what feels like longer. 
  • Pregnancy - Pregnancy hormones are activated during pregnancy, and this can trigger more REM sleep. This can combine to result in dreams that have a more unrealistic effect. 
  • Mental disorders - Disorders such as PTSD, anxiety and depression can influence dreams or nightmares. Some scientists believe that the past trauma or stress related to these disorders may link these dreams to memories or subconscious emotions.

This shows how our mental and physical conditions can impact and influence our dreams.


Croissant and tea on bed

The most common food people associate with bad dreams is cheese! Although this may just be an old wives tale, some people suspect that the types of food you eat before bed may actually affect your dreams. 

There is no solid evidence to support this, but if you eat foods such as carbohydrates closer to bedtime, it could potentially affect your body as you sleep. Most people recognise times when they have felt a wall of tiredness hours after eating carbohydrates or coming down from a sugar high. The effects on your body and brain can be a feeling of lethargy and difficulty in concentrating.

If these factors affect your body and brain while your awake, what happens if you eat these foods closer to bedtime? Could sugar-crash or post-carbohydrates slump influence how we dream? Unfortunately, we have no evidence for this theory, but it is an interesting thought.


If you’d like to dream or have nightmares less, then doing more exercise may help for the following reasons:

  • Exercising relieves stress - This can help you fall asleep faster as you have fewer worries to keep you awake.
  • Exercise promotes deeper sleep - As your body needs to repair and relax to recover from your workout, it requires more time in deep sleep and less in light sleep. REM sleep is one of the lightest stages of the sleep cycle, so exerting your body more will keep you in deep sleep for longer.
Woman stretching before a run

What are nightmares?

Nightmares are dreams that are often scary or upsetting. You’re more likely to have a more emotional or physical reaction when you wake up from a nightmare. 

This can include: 

  • Sweating
  • Heavy breathing
  • Increased heart rate
  • Being unable to get back to sleep

To find out more about why we have nightmares and how you could stop them, check out the sections below. 

Why do we have nightmares?

Similar to ‘why do we dream?’, we’re still not entirely sure why we have nightmares, but there are two main compelling theories about what causes nightmares:

  • Stress and anxiety 
  • Trauma

These go hand-in-hand with the idea that dreams are influenced by our subconscious emotions and memories. The trauma and internal stress we experience may feed into dreams, making them more frightening and disturbing.

If you’re worried about the number of nightmares you’re having, please talk to a doctor or healthcare professional.

Girl scared in bed

Side effects of nightmares

Most of the time, nightmares are just one-off dreams which may disturb your sleep for a night or so. However, some people experience ongoing side effects, such as:

  • Daytime sleepiness
  • Anxiety about going to sleep
  • A disrupted sleep pattern
  • Affected mood
  • Sleep deprivation 
  • Worse nightmares after sleep deprivation

In some cases, a more serious side-effect of nightmares is that they may lead to sleeping disorders. If you are worried about this at all, speak to your doctor.

How to stop nightmares

There are some ways you can try to stop your nightmares if you have them frequently. Here is a list of our top tips for how to stop nightmares:

1. Create a sleep schedule

Follow a strict sleep schedule to avoid sleep deprivation and the vivid dreams that follow from sleep deprivation

2. Don’t consume stimulating media before sleep

Be aware of the media you consume before sleep, and avoid content that is likely to stimulate your brain. Examples of this include horror or action films and games or video content.

Woman watching horror film on laptop

3. Exercise more

When your body recovers from a workout, you will spend more time in deep sleep rather than in the dreaming stages of sleep.

4. Make time to wind down

By taking the time to fully relax and calm your mind, you may find yourself feeling less stressed. A calmer emotional state may help to stop your nightmares.

5. Talk to your doctor

If you feel like your nightmares are triggered by trauma, anxiety or depression, seek professional help.

How to remember dreams

We’ve all woken up from a dream and thought that we’d had the best idea for the next best-selling book or blockbuster film, only to forget it instantly? Well, we have some tips to help you remember some of your best dreams!

  1. Tell yourself as you fall asleep that you want to remember your dream as you fall asleep - this keeps the thought fresh in your head when you wake up.
  2. Write down exactly what you’re thinking as soon as you wake up - pen and paper may work best as the distraction of unlocking your phone and opening an app may make you forget.
  3. Try not to use an alarm if you can - alarms interrupt your sleep and your thoughts which can cause you to forget them immediately.
Woman writing in sleep diary

The dreams that you remember are only the ones you’re dreaming of as you wake up. It’s also important to know that you’re less likely to recall your dreams if you sleep through the night undisturbed. This is because you’re not experiencing as much light sleep (REM sleep), which is when you dream the most.

Types of dreams

While there are many different types of dreams, here are three main types of dreams you may experience.

Vivid dreams

As previously mentioned, our most vivid dreams occur during rapid eye movement (REM) sleep. These dreams often seem the most realistic but may also be the most surreal. This may be because dopamine production in your brain is increased during sleep and dopamine has been linked to hallucinations.

Lucid dreams

Lucid dreams are dreams but you are aware that you are currently dreaming. It is suspected that people with more imaginative and creative minds find lucid dreaming easier than others. In these dreams, you can theoretically do whatever you want in your dreamscape until you wake up.

Common dreams

There are some dreams that most people experience regularly, such as:

  • Flying
  • Falling
  • Being chased

We’re not sure why most people share these similar dreams, but if you’d like to know more about these common dreams, why not check out our post where a dream expert reveals the meaning behind them?

Now you know all the different theories about why we dream and why we have nightmares! We hope you’ve learned more about how you dream, the science of dreams, and how you could influence your dreams.

If you’re looking to make more changes to your sleep, why not check out our extensive collections of mattresses, beds and accessories today?