Many people look forward to weekends as a chance to catch up on sleep and fully recharge. Yet, ironically, after the weekend ends and a new week begins, they often feel as if they've returned from a long journey—exhausted and drained. This fatigue tends to persist every morning until the weekend arrives again.
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The secret to sleep that truly revitalizes lies in a specific stage known as deep sleep. According to the U.S. National Sleep Foundation, not getting enough deep sleep leads to grogginess, drowsiness, reduced alertness and concentration, difficulty learning and forming new memories, and intense cravings for high-calorie foods.
The Stages of Sleep
When a person falls asleep, their body goes through three stages of non-REM (Non-Rapid Eye Movement) sleep, followed by one stage of REM (Rapid Eye Movement) sleep, as reported by Al Jazeera Net.
In the first half of the night, the body spends more time in non-REM sleep. As the night progresses, REM sleep becomes more dominant.
Stage 1 is a short transitional phase from wakefulness to sleep, marked by slowing heart rate and breathing.
Stage 2 involves a further decrease in heart rate and body temperature, along with muscle relaxation. This stage grows longer throughout the night and makes up about half of total sleep time.
Stage 3 is deep sleep, where brain waves are at their slowest frequency and highest amplitude. Breathing and heart rate are very slow, muscles are deeply relaxed, and it becomes difficult to wake the person. Waking from deep sleep can cause mental fog for up to an hour.
After these stages, the body enters REM sleep, during which the eyes move rapidly under closed lids and brain activity resembles that of someone awake, though the muscles remain still. Most dreaming occurs during this phase.
A full cycle through all four stages takes approximately 90 to 120 minutes, and adults typically experience 4 to 6 sleep cycles per night.
The Importance of Deep Sleep
All sleep stages are important for maintaining health, but deep sleep has distinct benefits. During this phase, the body releases growth hormone and works to build and repair muscles, bones, and tissues. It also strengthens the immune system. In addition, slow-wave sleep plays a critical role in glucose metabolism regulation, cognitive function, and memory.
Deep sleep is also believed to be important for learning languages, developing motor skills, and supporting brain development. A study published in JAMA Neurology showed that a lack of deep sleep may have long-term consequences on cognitive health. Research from Monash University and the Turner Institute for Brain and Mental Health in Melbourne, Australia, found that insufficient deep sleep may increase the risk of dementia.
How Much Deep Sleep Do You Need?
While adults are generally recommended to get at least 7 hours of sleep per night, about 20% of that time is ideally spent in deep sleep. Deep sleep typically begins within an hour of falling asleep, with its duration decreasing as the night goes on.
The body self-regulates deep sleep. For instance, someone recovering from sleep deprivation will spend more time in deep sleep. Conversely, those who sleep regularly and adequately may require less deep sleep at night because their needs have already been partially met during the day.
Older adults naturally get less deep sleep, often compensating with longer durations in stage 2 sleep.
How to Improve Deep Sleep
You can increase the amount of deep sleep—and in turn, your energy and focus—by following some simple habits, according to The Telegraph:
Stick to a consistent sleep schedule, even on weekends. The body operates on a 24-hour internal clock, and regular sleep-wake times help align all organs and cells to function efficiently.
Create a calming bedtime routine, limit screen time before bed, and ensure your sleep environment is dark and quiet.
Avoid caffeine and heavy meals late at night, and stay active during the day to promote better sleep quality at night.
Ultimately, it’s not just about how long you sleep—but how well.
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