Slow wave sleep: what is it, and why is it so important for your mental health?

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Hannah-Rose Yee
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Experts are calling it one of the most underrated heroes of your rest cycle. This is why slow wave sleep is so important. 

Once, sleep was considered to be one long, relatively passive stretch of rest. You got in bed, you fell asleep, you woke up. Rinse, repeat.

Now, thanks to the surge in interest in the concept of sleep from a health and wellness point of view, we have a better idea of what happens to our body while we snooze. Our cells repair, our short term memory is fortified, our brains are creative and active. Sleep is a pretty incredible time for the human body – and it all happens while we’re dozing in bed.

There’s a big difference between the various kinds of sleep, though. Most people know about REM sleep, or the Rapid Eye Movement section of a rest cycle where you do the most of your nightly dreaming. It’s long been considered an integral part of the sleep cycle, but recently there’s been an increase of interest in slow wave sleep, a very different kind of rest. 

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Here is everything you need to know about slow wave sleep…

What is slow wave sleep? 

how to get to sleep
Are you paying enough attention to slow wave sleep?

The simplest way of understanding it is to look at slow wave sleep as the deepest part of your sleep cycle. Before your body slips into REM mode, it moves through three different kinds of non-REM sleep. The first, and the shortest, is when you are likely to be in the lightest part of your sleep, while the third is the deepest. Basically, your brain slows down progressively over each of these three stages until you are well and truly out for the count.

The middle stage, or N2 as scientists call it, is believed to be the component of your sleep routine when memories are cemented. N3, or slow wave sleep, is what you move into after that cycle is complete and you’re ready to dream in the REM phase. It’s a deep, solid sleep that usually lasts for around 40 minutes and comes with lots of physical and psychological benefits. But it can also be the place when sleep disorders are most likely to crop up.  

Why is slow wave sleep so important? 

woman asleep
Don't underestimate the power of slow wave sleep for your health and wellness.

Slow wave sleep is deep and restful: your brain quietens down, your heart rate and breathing slow to the lowest point during the evening and there is no eye movement. Because of this, slow wave sleep is crucial to feeling like you’ve had a good night’s rest. Have you ever arisen from bed in the morning feeling sluggish and more tired than ever? You probably had a disruption to your slow wave sleep during the night.

During the non-REM cycles, and in particular in slow wave sleep, your body goes about the healing and regenerative processes that help strengthen your immune system, hormones, cells and mental health. Slow wave sleep is also the time in which information learned during the day is stored and processed by the brain. These actions are vital to a healthy body and mind and serve as a reminder to pay attention to the slow wave sleep portion of your rest cycle. 

“Before, REM got a lot of focus,” Dr Sheri Jacobson, director of Harley Therapy explains. “They are both important.”

Jacobson adds that getting deep, restful slow wave sleep is vital to your overall health. For example, take the important regenerative work that takes place during slow wave sleep. “If you’re in physical shape, you’re able to do so much more,” Jacobson explains. “If you’re able to fight infection, if your body is able to heal and repair better, then that is a big aid to mental health. The two aims are connected. Our body and our behaviour are all interlinked. If one of those links gets a chink in it, the whole cycle can dip.” 

What are some problems that can occur during slow wave sleep? 

Nightmares and sleepwalking are most likely a result of disruption to slow wave sleep.

If you suffer from nightmares, night terrors or sleepwalking, you are most likely experiencing a disruption to your slow wave sleep cycle.

More broadly, though, not having enough slow wave sleep is about not getting enough deep rest, which will have serious impacts on your body. “Sleep is an evolutionary necessity,” Jacobson says, “We can go without food and water for certain periods of time, but if we go with extended amounts of sleep deprivation usually there is some significant effect.”

You might notice your immune system slowing down or a breakdown physiologically in how your body heals and repairs. You might notice problems with processing emotions and memories. You might see hormonal issues. You might even see mental illness, given that there has been significant research linking a lack of sleep with a rise in anxiety (weighted blankets could help), depressive episodes and other problems with your mental health.

Sleep is absolutely crucial to our bodies and our minds, and slow wave sleep is an important part of that process.  

How can we improve our slow wave sleep? 

More than 70% of people sleep better after giving up booze for a month. 

According to Jacobson, we all need between seven and nine hours of sleep. (The exact amount varies from person to person.)

The best thing to do, she says, is to establish a sleep hygiene routine and stick to it. Jacobson calls it “good sleep habits”, or the little things that you do in the evening that help you have a restful night. It could be as simple as reducing your screen time in the evening, winding down with some relaxing music and a bath or shower. It might mean thinking about the light and noise pollution in your bedroom and working on reducing them. It might mean cutting back on caffeine and alcohol in the evening, or changing what you do right before bed. (As a general rule: no TV and nothing too stimulating.)

“It’s really unique,” Jacobson says. “So it’s about experimenting with what makes a good sleep hygiene practice for you, adopting it, and practicing it regularly.” 


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The most important thing, Jacobson says, is to make sure that you don’t increase the changes of sleep anxiety by putting even more pressure on yourself to have it. “Don’t observe every minute of sleep, or lack of it,” she says. “Sleep tracking devices are helpful, but they can contribute to the problem of watching and monitoring every moment of sleep. For some people, it might be best to let go of that.”

She adds: “You can easily get into a sleep worry spiral, where it becomes harder and harder to get to sleep. You’re monitoring your sleep levels, your self-criticising and you’re adding negative thoughts and self-judgement along the way.”

Jacobson’s solution is thus: “Honour your body’s need for sleep. But don’t put too much pressure on yourself. Be compassionate.

Images: Getty, Unsplash


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Hannah-Rose Yee

Hannah-Rose Yee is a writer based in London. You can find her on the internet talking about movies, television and Chris Pine.

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