Have you ever wondered what happens when you close your eyes and drift off into the night? Sleep, an essential yet enigmatic part of our lives, is more than just a period of rest. It's a dynamic adventure through various stages, each with its unique characteristics and importance to our well-being. Today, we're going to demystify this nocturnal voyage, breaking down the phases of sleep into bite-sized, easy-to-understand pieces.

Let’s get to the basics. Sleep can be divided into two broad categories: NREM (Non-Rapid Eye Movement) and REM (Rapid Eye Movement). These categories are like two different worlds our mind travels through at night, each playing a vital role in how rested we feel the next day. 

NREM Sleep: The Foundation of Our Nightly Journey

NREM sleep is what we first enter upon falling asleep, and it's partitioned into three distinct phases (known simply as N1, N2, and N3). See them as the different floors that lead you deeper and deeper into your “Sleep Palace”.

1. N1, the lightest phase of sleep, serves as a bridge between wakefulness and sleep. In this stage, which lasts for about 1-5 minutes/cycle, our body begins to relax, our heartbeat and breathing slow down, but we can be easily awakened. You can probably recognize it, it's that fleeting moment where you're not quite asleep but no longer fully awake.
2. Progressing into N2, we drift into a more stable state of sleep. Our body temperature drops by about 1 to 2 degrees Fahrenheit, and our muscles relax even further. This phase lasts for about 20 minutes/cycle and occupies the largest portion of our nightly sleep cycles. It's here that our body starts serious repairs and regrowth, kickstarting the process that is then continued by N3, the phase of deep, restorative sleep. 
3. N3 is the hardest phase to be woken up from - at this point, you are deep into the chambers of your “sleeping palace”. Your body focuses on repairing muscles and tissues, strengthening the immune system, and building energy for the next day. This phase initially lasts for 20-40 minutes but shortens with each sleep cycle throughout the night.

REM Sleep: The Dream Stage

After descending through the depths of NREM sleep, we ascend into the REM phase. This phase is usually known for being the stage where most dreaming occurs. Our brain activity increases, resembling that of being awake, our eyes dart back and forth beneath closed lids – hence the name "Rapid Eye Movement". However, despite this flurry of brain activity, our muscles remain in a state of deep relaxation, almost paralyzed, to prevent us from acting out our dreams.

The first iteration of REM in you nightly journey might last only a short time but, with each cycle, it becomes longer, stretching up to an hour per-cycle as dawn approaches. Studies show that REM sleep plays crucial roles in learning, memory consolidation, and emotional regulation.

The Rhythm of the Night: Cycling Through Stages

Now that we know how these individual phases work, we can get into how they concatenate together. Across a typical night, a sleeper will travel through four to five cycles of NREM and REM stages, starting with N1, following with N2 and then moving further down to N3, then back up to N2 before entering REM. The cycles repeat approximately every 90 to 110 minutes and the amount of time taken up by each phase will change throughout each.

Understanding these phases reveals the importance of both quantity and quality of sleep. For example, missing out on deep N3 sleep or cutting short the REM phase can leave you feeling tired and foggy, even after a long night's rest.

What we hope you take away from this little journey is that sleep is not simply a passive state but a rich, complex process that supports nearly every aspect of our health. Never forget, understanding your sleep is the first step towards improving it, so if reading this is making you want to change things up, head on over to the next article Prioritizing the Power of Sleep, and find out about 6 Golden Rules to get you started. Sweet Dreams!

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 References:

• Patel AK, Reddy V, Shumway KR, et al. "Physiology, Sleep Stages.", National Library of Medicine, January 2024, https://www.ncbi.nlm.nih.gov/books/NBK526132/
• Ambardekar Nayana, "What Happens to Your Body When You Sleep?", WebMD, March 2021, https://www.webmd.com/sleep-disorders/what-happens-body-during-sleep

Any questions or comments, drop a note to the DEEPS Blog Team on the Contact us page.