Why do you get nightmares? How do you calm down and go back to sleep after a really bad one?

Your heart’s racing and your rumpled sheets are soaked in perspiration. It’s a little past 4am and there are a good few hours before you have to be up. But you can still feel the tendrils of the nightmare that ensnared you from sleep. Your day has started in Disturbia before the sun is up.
People ascribe all sorts of meanings to nightmares – a message from a deceased loved one, a premonition of some disaster, a warning not to go with a certain decision, and a personal favourite, an excuse not to get out of bed or the world will end.
The scientific explanation for their causes? Mainly unresolved fears, stress or traumatic experiences that reflect internal conflicts or suppressed emotions from your waking life.
“The brain weaves together recent experiences and past memories, and when heightened emotions like fear, anxiety or frustration are involved, dreams can take the form of nightmares,” said Dr Alla Demutska, the clinical director of counselling and psychotherapy at The School of Positive Psychology.
“Nightmares are particularly linked to emotional upheavals or mental health issues such as post-traumatic stress disorder (PTSD), anxiety and depression, signalling that the mind is working to process difficult emotions or unresolved psychological conflicts,” she said.
No one enjoys these personal screenings of horror shows during sleep, and if you’re trying to minimise your nightmare’s impact on you by rationalising them, here’s what the experts say:
According to Sleep Foundation, you go through four stages of sleep each night: Three non-rapid eye movement (or NREM) sleep phases that take you from light to deep sleep, and one REM sleep phase.
“Dream-like mental activity can be observed during all sleep stages – it’s only during REM sleep that dreams are particularly vivid and intense,” said Dr Amanda Chan, a senior consultant with National University Hospital’s Department of Medicine, Division of Neurology.
Dr Demutska added that REM sleep usually begins 90 minutes after you fall asleep. “During REM sleep, the brain becomes highly active, with increased activity in areas responsible for processing emotions and memories as well as the visual cortex.”
You dream daily but will only remember the dream or nightmare if it wakes you up, said Adrian Lau, the principal psychologist at Mount Elizabeth Hospital. So, it all comes to bear that light sleepers or those who don’t sleep well tend to recall more nightmares. “If a nightmare is emotionally intense, such as frightening enough to wake someone with crying or shouting, the person will likely remember it,” said Lau.
Age also plays a part. Individuals between 20 and 39 years of age have a high prevalence of nightmares – and it decreases from age 50 onwards, said Dr Chan. “The reduction in nightmare frequency may be due to improved emotional regulation, reduced REM sleep, decreased imagination, and the ability to manage stress more effectively,” she said.
Interestingly, the incidence of nightmares may rise again to around 6.3 per cent, particularly in those over age 70, said Dr Demutska. It is often linked to factors like deteriorating physical health, cognitive decline, stress or depression, she said.
Night terrors terrorise the dreamer during deep, NREM sleep. “During a night terror, the person is difficult to wake,” said Dr Demutska. “These episodes are most common in children and can be distressing for caregivers, though the child is not conscious of the fear they exhibit.”
And yes, adults can get night terrors, too. You may wake with no memory of the event but your partner will let you know that you were screaming, thrashing or even sleepwalking the night before, said the experts.
According to the American Academy of Sleep Medicine, approximately 2 per cent of adults experience night terrors. “We do not know why adults have fewer night terrors, but perhaps it is due to their ability to better manage distressing experiences, which are associated with night terrors in children,” said Dr Chan.
“If broken sleep leads to insufficient rest and fatigue during the day, it’s time to see a doctor,” advised Lau. “People with sleep disorders should seek help if the issue persists for more than a week. Nightmares may also be a symptom of PTSD, in which case, psychological help may be necessary for unresolved trauma,” he said.
Other signs that there could be an issue include frequent nightmare episodes (more than once a week), avoidance of sleep, or increased anxiety around bedtime, said Dr Demutska.
“One should seek medical attention when there are repeated occurrences of extended, extremely dysphoric and well-remembered dreams that usually involve threats to survival, security or physical integrity,” said Dr Chan.
“This can depend a lot on your beliefs,” said Lau. “If you believe dreams foretell the future, it will be harder to relax.” What you can try, said Lau, is remind yourself that the content of the nightmare is random, and has no bearing on real life. 
As you’re engaging in the self-talk, ground yourself in the present by focusing on the details in your room, said Dr Chan. Take slow and deep breaths, and engage your senses by noticing the sensory details around you, she said. “Touch something physical that acts as a comforting object to anchor yourself in the present reality.”
To help ease your mind further, suggested Dr Demutska, keep a notepad next to your bed. “When you wake up, jot down a keyword or phrase that captures the nightmare. Nightmares are often messages from the unconscious mind, attempting to get our attention. By writing down a few words, you externalise those thoughts, which can help reduce the mental load and stress.”
“To fall back asleep more comfortably, change into a new set of clothes if what you’re wearing got damp from sweating,” Lau suggested.
Then, try deep, diaphragmatic breathing, recommended Dr Demutska, to activate your parasympathetic nervous system, which will help to calm your body. “If this doesn’t work, briefly getting out of bed may help reset your nervous system. Light stretches, drinking water, or reading something non-stimulating can also be effective in shifting your focus away from the nightmare,” she said.
If you need to get out of bed or check the time, avoid bright lights, said Dr Chan, as they can disrupt melatonin production and make it harder to fall back to sleep.
Start your day with a to-do list to give yourself a sense of purpose, recommended Lau. “This helps distract from the nightmare and keeps you focused. People who live purpose-driven lives with plenty of interests find it easier to shake off bad dreams.”
It is also a good idea to engage in movement such as yoga or stretching to help reduce lingering tension in the body, said Dr Demutska. “Engaging in a gratitude practice or adopting a positive mindset shift can set a more intentional tone for the day.”
“Nightmares cannot be prevented,” said Lau. “It is important not to be afraid of nightmares, or else, one may end up being scared to fall asleep in order to avoid it.” To increase your chances of getting a good night’s sleep without waking up in the middle of a nightmare, create your own bedtime routine to train your brain to be ready to rest, he suggested.
For instance, after a stressful day or during a difficult period, try calming activities like reading, listening to soothing music, practising deep breathing, or meditating to help relax your nervous system, advised Dr Demutska. “Avoid watching intense or scary content right before sleep, as it can trigger nightmares.”
Keeping a consistent sleep-wake cycle, even on weekends, can improve your sleep quality and reduce the chance of nightmares, she said. “Consistency helps regulate your body’s internal clock.”
Regular exercise may be helpful to alleviate nightmare-causing anxiety and stress, said Dr Chan. “Also, be cautious about the use of alcohol, caffeine and nicotine, which can remain in your system for more than 12 hours and often disrupt sleep patterns.”