Deep sleep, what it is and how to get more of it

The lamp is off, the house has gone quiet and your breathing slows. Within the first hour, you sink into the deepest sleep of the night [1]. You won't remember it, though by morning it has done some of the night's most useful work.

Deep sleep is the stage of slow, large brain waves that comes mostly in the first half of the night [2]. You can't force it, but trials point to a few things that help, such as daytime exercise, an earlier last coffee, a warm bath and a cool bedroom. This guide follows them through the day, then looks at REM sleep, sound devices and hypnosis.

What is deep sleep?

Deep sleep is stage 3 of non-REM sleep, also called N3 or slow-wave sleep. It's named after its slow, large brain waves, which are measured in a sleep lab [2].

Through the night you move through light sleep, deep sleep and REM (rapid eye movement) sleep in cycles of about 60 to 90 minutes. Most deep sleep comes in the first half of the night, and most REM sleep in the second half [1].

Why is deep sleep important?

Deep sleep is when much of the day's learning is turned into long-term memory. It's also when the body releases most of its growth hormone, which helps with repair [2].

Your body also seems to protect it. After a night of lost sleep, the next night brings more slow waves [2]. So one short night is usually followed by deeper sleep.

How much deep sleep do you need?

In adults, deep sleep makes up about 18 to 22% of the night [2]. Our guide to how much deep sleep you need covers typical amounts and how far to trust a sleep tracker.

How to get more deep sleep

These steps follow the day, from morning to lights out. Most were tested in healthy adults.

In the day, move more

A review of 66 studies found that a single session of exercise brought small gains in deep sleep. Regular exercise helped people sleep a little longer and rate their sleep better [3].

Evening exercise is usually fine. A review of 23 studies in healthy adults found it didn't harm sleep and slightly raised deep sleep. Hard exercise that ended an hour or less before bed might make it harder to drop off [4]. In a later review of 28 studies, moderate evening exercise did best for deep sleep, though the result was uncertain, and hard exercise cut REM sleep [5].

After lunch, watch the caffeine

In a review of 24 studies, caffeine cut deep sleep by about 11 minutes and total sleep by about 45 minutes. The authors suggest having a regular coffee at least 9 hours before bed [6]. For a 10pm bedtime, that's a last coffee around 1pm.

In the evening, try a warm bath

A review of 17 studies looked at warm baths and showers of 40 to 42.5°C. Taken 1 to 2 hours before bed, for as little as 10 minutes, they helped people fall asleep faster and rate their sleep better [7]. In an older study of six women, a long hot afternoon bath raised deep sleep that night [8].

At bedtime, keep the room cool

Heat makes you wake more and cuts both deep sleep and REM, and humid heat makes it worse. Bedding and nightclothes matter too, because they set the warmth right next to your skin [9]. So tonight, try a lighter duvet and an open window if the room feels warm.

Go easy on alcohol

A drink can feel like a shortcut to deep sleep. It does help you drop off and adds deep sleep in the first half of the night, but it breaks up the second half. It also delays REM sleep and, at moderate and higher amounts, cuts it [10].

Why am I not getting much deep sleep?

Age plays a part. In a study of 149 healthy men, deep sleep fell sharply between early adulthood and midlife, with lighter sleep taking its place [11]. A newer review notes that studies using today's scoring rules found no clear fall with age, so the picture is mixed [2].

Sleep apnoea is another cause, where your breathing stops and starts while you sleep. The NHS says to see a GP if this happens, if you make gasping, snorting or choking noises while asleep, or if you always feel very tired during the day [12].

Deep sleep vs REM sleep

Deep sleep comes mostly early in the night, while REM comes mostly in the second half [1]. So cutting your night short with an early alarm costs you REM more than deep sleep.

To get more REM, give yourself a full night, and go easy on alcohol, which delays and cuts it [10]. Hard exercise late in the evening also cut REM in one review [5].

Do sound devices and hypnosis help?

In sleep labs, soft sounds timed to the brain's slow waves can boost them [2]. A review of 10 studies found only a small, uncertain effect on memory, and the authors said the evidence isn't strong enough to recommend devices sold for home use [13].

Hypnosis has been tested in daytime naps. Hearing a recorded suggestion to "sleep deeper" raised deep sleep in young and older women who were easily hypnotised, but not in those who weren't [14][15].

Where Nooroots fits

Nooroots Triple Magnesium is a food supplement with magnesium glycinate, citrate and malate, in three capsules a day. Magnesium contributes to normal psychological function and to a reduction of tiredness and fatigue [16].

Frequently asked questions

What stage of sleep is deep sleep?

Deep sleep is stage 3 of non-REM sleep, also called N3 or slow-wave sleep [2].

When do you get the most deep sleep?

Mostly in the first half of the night, often starting within the first hour after you fall asleep [1].

Does alcohol help you get deep sleep?

It adds deep sleep early in the night but breaks up the second half and delays REM sleep, so the night as a whole is more broken [10].

Can you catch up on deep sleep?

Partly. After a short night, the next night brings more of the slow waves that mark deep sleep [2].

Is deep sleep or REM more important?

Both matter, and you get both in a full night. Deep sleep comes mostly early and REM mostly later, in cycles of about 60 to 90 minutes [1].

Does deep sleep hypnosis work?

In nap studies, a recorded suggestion to sleep deeper raised deep sleep only in people who were easily hypnotised [14].

Read more about settling at night in our guide on how to fall asleep fast.

References

Every source here is listed so you can read it yourself. This guide is for general information and doesn't replace advice from your GP. We check it again at least every six months.

1. Carley DW, Farabi SS (2016). Physiology of Sleep. Diabetes Spectrum 29(1): 5-9. PMID 26912958
2. Ishii T, Taweesedt PT, Chick CF, O'Hara R, Kawai M (2024). From macro to micro: slow-wave sleep and its pivotal health implications. Frontiers in Sleep 3: 1322995. PMID 41424515
3. Kredlow MA, Capozzoli MC, Hearon BA, Calkins AW, Otto MW (2015). The effects of physical activity on sleep: a meta-analytic review. Journal of Behavioral Medicine 38(3): 427-49. PMID 25596964
4. Stutz J, Eiholzer R, Spengler CM (2019). Effects of Evening Exercise on Sleep in Healthy Participants: A Systematic Review and Meta-Analysis. Sports Medicine 49(2): 269-287. PMID 30374942
5. Yue T, Liu X, Gao Q, Wang Y (2022). Different Intensities of Evening Exercise on Sleep in Healthy Adults: A Systematic Review and Network Meta-Analysis. Nature and Science of Sleep 14: 2157-2177. PMID 36540196
6. Gardiner C, Weakley J, Burke LM, Roach GD, Sargent C, Maniar N et al. (2023). The effect of caffeine on subsequent sleep: A systematic review and meta-analysis. Sleep Medicine Reviews 69: 101764. PMID 36870101
7. Haghayegh S, Khoshnevis S, Smolensky MH, Diller KR, Castriotta RJ (2019). Before-bedtime passive body heating by warm shower or bath to improve sleep: A systematic review and meta-analysis. Sleep Medicine Reviews 46: 124-135. PMID 31102877
8. Horne JA, Reid AJ (1985). Night-time sleep EEG changes following body heating in a warm bath. Electroencephalography and Clinical Neurophysiology 60(2): 154-7. PMID 2578367
9. Okamoto-Mizuno K, Mizuno K (2012). Effects of thermal environment on sleep and circadian rhythm. Journal of Physiological Anthropology 31(1): 14. PMID 22738673
10. Ebrahim IO, Shapiro CM, Williams AJ, Fenwick PB (2013). Alcohol and sleep I: effects on normal sleep. Alcoholism: Clinical and Experimental Research 37(4): 539-49. PMID 23347102
11. Van Cauter E, Leproult R, Plat L (2000). Age-related changes in slow wave sleep and REM sleep and relationship with growth hormone and cortisol levels in healthy men. JAMA 284(7): 861-8. PMID 10938176
12. NHS. Sleep apnoea. Page last reviewed 11 May 2026. Accessed 30 October 2026. nhs.uk
13. Wunderlin M, Züst MA, Hertenstein E, Fehér KD, Schneider CL, Klöppel S et al. (2021). Modulating overnight memory consolidation by acoustic stimulation during slow-wave sleep: a systematic review and meta-analysis. Sleep 44(7): zsaa296. PMID 33406249
14. Cordi MJ, Schlarb AA, Rasch B (2014). Deepening sleep by hypnotic suggestion. Sleep 37(6): 1143-52, 1152A-1152F. PMID 24882909
15. Cordi MJ, Hirsiger S, Mérillat S, Rasch B (2015). Improving sleep and cognition by hypnotic suggestion in the elderly. Neuropsychologia 69: 176-82. PMID 25660206
16. Department of Health and Social Care. Great Britain nutrition and health claims (NHC) register, spreadsheet of 19 May 2026. Accessed 30 October 2026. gov.uk