Sleep is an essential part of our lives. Not only does it restore our bodies, but it is also crucial to our mental health and overall well-being. During a typical night, we go through several sleep stages, collectively known as the sleep cycle. In this blog, we will take a closer look at each stage of the sleep cycle and discover exactly what happens during sleep.

Phase 1: Falling asleep phase (NREM 1).

The sleep cycle begins with the sleep-in phase, also called NREM 1. This is a light sleep phase in which we transition from being awake to sleeping. During this phase, you may still be aware of your surroundings and wake up easily. Muscle activity slows down and your eye movements become less frequent. This phase usually lasts only a few minutes.

Stage 2: Light sleep (NREM 2).

After the falling asleep phase, we enter the second phase of the sleep cycle, known as NREM 2 or light sleep. In this stage, sleep becomes deeper, but you are still easily aroused. During NREM 2, your heart rate and breathing become more regular and your muscles relax further. This phase makes up the bulk of your total sleep time and can cover about half of a normal sleep cycle.

Stage 3: Deep sleep (NREM 3).

The third stage of the sleep cycle, NREM 3 or deep sleep, is the period of deepest and most restorative sleep. During this phase, your brain waves are slower and your muscles are completely relaxed. It can be difficult to wake up during this phase, and if you are awakened, you are likely to feel confused or disoriented. Deep sleep is crucial for physical recovery, muscle growth and a functioning immune system.

Stage 4: REM (Rapid Eye Movement) sleep.

The fourth and final stage of the sleep cycle is REM sleep, characterized by rapid eye movements, vivid dreams and increased brain activity. Although your muscles are temporarily paralyzed during REM sleep, your heart rate and breathing are irregular and accelerated. This phase is essential for event processing, memory and emotional well-being. It is also the phase when most dreams occur.

Repetition of the sleep cycle

During a typical night, our bodies go through several cycles of these four sleep stages, with each cycle lasting about 90 to 120 minutes. As the night progresses, the duration of REM sleep and light sleep increases, while the time spent in deep sleep decreases. This means that the first half of the night is primarily dominated by deep sleep, while the later half is more focused on REM sleep and light sleep.

How long does each sleep phase last?

This is how long each stage takes on average for adults:

• Falling asleep: 1 to 7 minutes in the first sleep cycle, which accounts for 5-10% of total sleep
• Light sleep: 10 to 25 minutes in the first sleep cycle and gets longer with each successive cycle, eventually making up between 45-55% of our total sleep
• Deep sleep: 20-40 minutes in the first sleep cycle and decreases as the night progresses. Deep sleep makes up about 15-25% of our total sleep.
• REM sleep: only 1 to 5 minutes in the first sleep cycle, but gets longer as you sleep more.

Waking up rested

There are different ideas about when is the best time to wake up. During a normal sleep cycle, there is often a brief moment of awakening between REM sleep and the next sleep cycle. That moment could possibly be the ideal time to wake up.  

Tip: Do you always wake up very tired or disoriented? Then it may well be that your alarm clock goes off exactly during your deep sleep. You can experiment by setting your alarm clock half an hour earlier or later. If you assume a 90-minute sleep cycle, it is ideal to wake up after 7.5 or 9 hours of sleep, when you come out of REM sleep.

Summary

The sleep cycle is an organized process that helps our bodies and minds repair and renew themselves. During a typical night, we go through several stages, from light sleep to deep sleep and REM sleep, all of which have important functions. A complete sleep cycle is essential for good health and well-being, and understanding these phases can help optimize your sleep pattern and wake up rested.

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Source: https://www.sciencedirect.com/science/article/abs/pii/0013469485900379