You know she's in deep sleep (slow-wave sleep) when her breathing and heart rate are slow and regular, muscles are fully relaxed, eye movement stops, and it's very hard to wake her; she'll likely feel groggy and disoriented if disturbed. Look for minimal movement, steady breathing, and a calm, still demeanor, contrasting with light sleep (eye movement) or REM sleep (rapid eye movement, faster breathing).
It is very difficult to wake someone during stages 3 and 4, which together are called deep sleep. There is no eye movement or muscle activity. People awakened during deep sleep do not adjust immediately and often feel groggy and disoriented for several minutes after they wake up.
Stage 3: Stage 3 sleep is deep sleep, which shows the greatest degree of relaxation in the body, as well as a specific pattern of slow brain waves. In this stage, your breathing and pulse are slow and steady.
Adults should aim to achieve about 20 percent of their sleep in the deep stage, which equates to approximately 60-100 minutes of deep sleep during an 8-hour night.
Typically, you'll see deep sleep on your sleep-tracking devices in the first half of your night. It happens in relatively long segments while your heartbeat and breathing slow to their lowest levels. You need about 1.5 to 2 hours of deep sleep each night.
Here are seven common signs that you may not be getting enough deep sleep:
11 tips to get more deep sleep and REM sleep at night
The 3-2-1 bedtime method is a simple sleep hygiene strategy: stop eating 3 hours before bed, stop working 2 hours before bed, and stop using screens (phones, tablets, TVs) 1 hour before sleep, helping your body transition to rest by reducing stimulants and digestive load for better sleep quality. A more detailed version adds 10 hours (no caffeine) and 0 (no snoozing) for a 10-3-2-1-0 rule.
During deep sleep, you pay less attention to the outside world. But while you may be out like a light, some parts of your body are hard at work. Your breathing and heart rate go down, but your ability to fight germs and to form memories goes up. Experts are still figuring out exactly what deep sleep is for.
Signs of poor core sleep (deep, restorative sleep) include waking up foggy, daytime fatigue/energy crashes, poor concentration, irritability, frequent illness, memory issues, and mood swings, indicating your brain and body aren't fully repairing and consolidating memories. You might also experience increased sugar cravings, slow muscle recovery, and a weakened immune system.
Polysomnography, known as a sleep study, is a test used to diagnose sleep disorders. Polysomnography records your brain waves, the oxygen level in your blood, and your heart rate and breathing during sleep. It also measures eye and leg movements.
Hypersomnia is excessive sleepiness. There are many causes of excessive sleepiness, including insufficient or inadequate sleep, sleep disorders, medications and medical or psychiatric illnesses. The characteristics of hypersomnia vary from one person to the next depending on age, lifestyle and underlying causes.
Melatonin, a hormone your body makes to help with your sleep cycle. It can also be found naturally in some foods. Good sources: tart cherries like Montmorency cherries, unsweetened tart cherry juice, eggs, milk, pistachios and almonds. Potassium and magnesium, nutrients that help promote muscle relaxation.
REM sleep occurs after deep sleep, usually 90 minutes after you fall asleep. Its conclusion marks the end of a sleep cycle (the average person completes four to six sleep cycles a night). During the first sleep cycle of the night, the REM stage lasts about 10 minutes.
While it's true that during some sleep stages our brains pay very little attention to what's happening around us, during other stages we're able to hear and process sounds even in our sleep. Not only that, but we are listening for certain sounds while we sleep, even when we're in deep sleep.
The third and fourth stages are deep sleep. Though REM sleep was previously believed to be the most important sleep phase for learning and memory, newer data suggests that non-REM sleep is more important for these tasks, as well as being the more restful and restorative phase of sleep.
Recognizing the Signs of Deep Sleep
The rarest major sleeping position is often cited as the Starfish (on your back with arms up), with only about 5-7% of people sleeping that way, but stomach sleeping (prone position) is also very uncommon, with less than 10% of adults preferring it, making it a strong contender for rarest, though sometimes considered a major type, not just a variation. More niche or minor variations, like specific fetal or "T-Rex arms" (bent wrists), might be rarer still, but data focuses on broad categories.
The koala is famous for sleeping around 20-22 hours a day, which is about 90% of the day, due to their low-energy diet of eucalyptus leaves that requires extensive digestion. Other extremely sleepy animals include the sloth (up to 20 hours) and the brown bat (around 20 hours), with some snakes like the ball python also sleeping up to 23 hours daily.
Our circadian rhythm functions by light and dark cycles and therefore an ideal sleep time is 10pm – 6am give or take ½ an hour either way so a full 8 hours of sleep is achieved each night. Even if you are retired or not working, this is an essential component of good sleeping habits.
Yes, the Navy SEAL sleep trick (an 8-minute power nap with elevated legs) is a real technique for quick rest, popularized by former SEAL Jocko Willink, that helps improve alertness and reduce fatigue, though its effectiveness depends on individual relaxation skills and it's not a substitute for full nighttime sleep. The method involves lying down, elevating your feet above your heart (on a chair or couch), relaxing facial muscles, dropping shoulders, and clearing your mind for about 8-10 minutes to promote relaxation and blood flow, preventing grogginess.
My personal routine is get ready for bed at 10pm (I sleep a lot so this can seem quite early), which involves: *taking meds *brushing teeth *unplugging everything in the house *Tidying room *preparing bags for the next day (although this could be part of a morning routine too) *getting into pyjamas *hanging clothes up ...
If you feel your total sleep time is adequate (between 7 to 9 hours per night) but you experience symptoms of sleep deprivation such as waking unrefreshed, difficulty focusing, learning, or carrying out everyday activities, it could be a sign of insufficient deep sleep.
Vitamin D helps control the sleep-wake cycle.
One way or another, we know that vitamin D is involved in parts of the brain that regulate sleep timing — including hormones that control the sleep-wake cycle. “For example, vitamin D seems to affect how much melatonin is made in the body.