The most important sleep stage is Stage 3, Non-REM or, Delta (Slow Wave) Sleep, it takes up 25% of our total sleep cycle, and it's known as the 'deepest' period of sleep. It's in Stage 3 that sleep is at its most restorative, helping our bodies heal themselves and our minds rest.
During deep sleep, your body works to repair muscle, organs, and other cells. Chemicals that strengthen your immune system start to circulate in your blood. You spend about a fifth of your night's sleep in deep sleep when you're young and healthy -- more if you haven't slept enough.
Subjectively, deep sleep is considered to be the most refreshing portion of the entire sleep cycle. It effectively erases the accumulated need for sleep that builds over a normal day of wakefulness, and may play a major role in helping clear the brain for new learning the following day.
An average sleep cycle lasts about 90 minutes. Ideally, you need four to six cycles of sleep every 24 hours to feel fresh and rested. Each cycle contains four individual stages: three that form non-rapid eye movement (NREM) sleep and one rapid eye movement (REM) sleep.
Sleep specialists believe that the last of them—known as deep sleep or slow-wave sleep—is the main time when your body renews and repairs itself. This stage of sleep appears to be the one that plays the greatest role in energy, enhancing your ability to make ATP, the body's energy molecule.
For healthy adults, 20-25% of your total time asleep should be REM sleep. That's where the 90-minute number mentioned above comes from. If you sleep for 7-8 hours, 20% of that equates to roughly an hour-and-a-half, or 90 minutes. However, it's worth noting that the amount of REM sleep we need also declines with age.
For healthy adults, spending 20-25% of your time asleep in the REM stage is a good goal. If you get 7-8 hours of sleep, around 90 minutes of that should be REM.
Multiple studies have shown that lack of slow wave sleep contributes to daytime grogginess and poor mood. Additionally, waking up during REM cycles interrupts our flow of aggregating memory. In order to make sure you wake up during light sleep, try and schedule your sleep in 90-minute multiples.
"In general, about 20% to 30% of the night [should be] in REM sleep, depending on age," Dr. Khosla explains. That's somewhere around 1.5 to 2.5 hours, if you sleep 8 hours a night. But you don't get it all in a single stretch; the time will be broken up into smaller chunks throughout the night, she says.
REM deprivation increases basal arousal and enhances drive-related behaviors like hyperphagia. It also affects physiological, psychological process as well as neurotransmitter levels. The mechanisms behind these changes are not fully understood.
So does snoring mean deep sleep? No it doesn't. REM sleep becomes very fragmented and interrupted by snoring so snorers aren't able to reach deep sleep. Only frequent, prolonged and severe snores mean possibly obstructive sleep apnea.
Some people with insomnia experience changes in their sleep cycles and, as a result, may have more stage 1 sleep and less deep sleep. Stress and aging can also reduce levels of deep sleep. Additionally, people with conditions such as schizophrenia and Alzheimer's disease experience less slow wave sleep.
Sleep Trackers Don't Measure Sleep Very Well
So, do FitBits, Apple Watches and Oura Rings track sleep with accuracy? The answer is, not really. Particularly when it comes to sleep stages. These wearables measure movement very well and are great when used for tracking steps and exercise.
Hypersomnia is usually indicated by long sleep periods and excessive sleepiness or excessively deep sleep. It may be associated with difficulty in awakening – the person may feel confused or disoriented (sleep drunkenness).
REM sleep happens about an hour to an hour and a half after falling asleep. REM sleep is when you tend to have vivid dreams.
Without a pillow, your head and neck can sag, constricting your airways. This can make breathing feel more labored, increase the risk of snoring, and aggravate symptoms of sleep apnea.
The bottom line: using large or too many pillows may be soft for your head but bad for snoring and breathing patterns. Make sure your pillow keeps your head tilted slightly backwards or in a neutral position.
Reisacher suggests sticking to one pillow, which can actually reduce snoring and keep your airway open. While you're looking for the cure to your snoring, remember that you can also block the noise with earplugs for sleeping.
A person may not remember the events of their dreams because they cannot access that information once they are awake. In a 2016 article in the journal Behavioral and Brain Sciences, researchers posit that people forget their dreams due to changing levels of acetylcholine and norepinephrine during sleep.
There are several reasons that you might not be getting enough deep sleep. Weakened sleep drive. Taking naps or spending too much time in bed can weaken your sleep drive. You may lose some of your ability to sleep normally, and as a result, you may get less deep sleep.