What happens when we sleep at night – 2 interesting facts

Introduction 

Ever wondered why we are sensible to sounds while dozing off, what happens when we sleep why waking someone up from sleep is so tough, and why we tend to have intense dreams in the morning, and where do we go when we sleep ?  And when we are lost in dreams, why can’t we speak out loud even if we try? If you’ve wondered about these nighttime mysteries, this blog is for you. 

This is all because of the variation in our sleep cycle. You know? Our sleep follows a structured pattern called sleep architecture. Let’s see the architectural design of sleep. what happens to your body when you sleep ?

Two flavours of sleep

In the fascinating journey of our sleep cycle, we go through two different stages: 

• NREM (Non-Rapid Eye Movement) sleep
• REM (Rapid Eye Movement) sleep

During the NREM stage, we dive into deep sleep while in the REM state, we experience adventures through dreams. NREM is further divided into N1, N2, N3 and sometimes N4 phases.

The journey through the cyclical rhythm of sleep

So, the cycle goes on like N1, N2, N3, N2 and REM and this is one cycle. Each cycle lasts for 1.5 – 2 hours. Throughout our sleep trip, we go through 4 -5 cycles but the duration of each phase varies. This variation in our sleep cycle is the key reason for our nighttime adventure cycle.

what happens when we sleep

Navigating the Sleep Cycle: Journeying from NREM to REM stages

The sleep cycle begins with the NREM stage, followed by the REM stage.

Driving through NREM sleep

N1 stage (Light sleep): Entering the hall of sleep

As we start to doze off, we enter into this initial phase (N1) which lasts 1 to 5 minutes. It’s a phase where we still remain sensitive to sounds. For example, even a soft whisper in the ear can easily wake us up from this light sleep.

Ever noticed someone dozing off in class, then immediately wake at the sound of a little noise?  This is a transitional stage between wakefulness and sleep, where our mind manages to stay alert even when sleep tries to take over. 

Hypnic jerks/Sleep start is the typical feature of this stage. When you start to fall asleep, your brain mistakenly assumes that you are really falling and reacts by jerking your muscles. Most of us would have felt this including myself.

N2 stage: Time to work on memory and cut off outside distractions

Moving from N1 and entering into the N2 stage: During this stage, your heart rate and temperature decrease, creating a sense of relaxation. In N2, one becomes disconnected from the external world as the senses are muted, making it a little hard to wake up someone.

You may have noticed that some people tend to grind their teeth in sleep. This activity is commonly seen in this stage. 

Memory shifting: Memories are shifted from the short-term storage area (Hippocampus) to the long-term storage area (cerebrum) in our brain during N2 and N3.

This stage lasts 10 – 25 minutes but its duration lengthens with each successive cycle. 

N3 stage (Deepest sleep): It’s repair time

Entering into a deep sleep: It lasts 20-40 minutes and waking someone from this stage is challenging. If a person wakes up from this stage that person will experience mental fog for 30 minutes to 1 hour. 

Recovery mode ON: It repairs and regrows the damaged part, builds muscles and bones and strengthens the immune system.

Cleaning time: During deep sleep, our brain’s cleaning system – Glymphatic system cleans away the waste from the brain including the beta-amyloid and tau protein responsible for Alzheimer’s dis-ease and makes us ready to face the next day’s challenges.

This stage of sleep also hosts the events of sleepwalking, night terrors, and bedwetting.

Entering REM sleep

REM sleep (Vivid sleep): Sail through the fantastical landscapes of dreams

Ever noticed someone rolling their eyes behind their closed eyelids in sleep? That’s the indication that the person is in the REM stage. During this stage, we ride through the waves of dreams including nightmares. 

You’ve experienced someone saying a horrible experience: “I was having bad dreams and cried out your name, didn’t hear me? It felt like someone was choking me, making me unable to move. Maybe this is the work of ghosts.”

No, ghosts aren’t the cause. During this stage, apart from muscles responsible for breathing, eye movement and heartbeat, all other muscles remain inactive to prevent us from physically responding to the unreal things we experience in dreams.

Since our voice is produced by muscles, we are unable to shout while dreaming, which leads to the sensation of throat pressure. This sensation makes us feel like someone is choking us. The muscle inactivity during this stage makes us feel like we are controlled by supernatural forces.

Dreams heal your emotional wounds by stripping away emotions from those memories. They often present solutions to the challenges you face in reality, helping you prepare to handle similar situations in the future.

Memory consolidation takes place during REM sleep. During this stage, our memories are recollected, connected, deleted and stored, which sculpts our past into our existence. So it’s like we go to sleep with an unsolved puzzle and wake up with a solution.

REM sleep improves our mental activity – processing, understanding, perceiving, reacting, storing and recollecting information and decision-making abilities.

Sexual arousal happens in this stage: Blood flow increases to the reproductive parts leading to the erection of the penis and clitoris. This is why we have wet dreams sometimes. 

As the night progresses, the duration of REM sleep increases and the NREM period decreases. This is the reason why we have dreams in the early morning.

Why do changes happen between the NREM & REM stages?

During the NREM stage, Heart rate, Temperature and Blood pressure are reduced to keep us relaxed and make us fall asleep. During the REM stage the Heart rate, Blood pressure and Temperature go up similar to the state of wakefulness. Additionally, our brain consumes more oxygen and remains active during this stage. These changes occur to protect our overall health.

“Hormones also fluctuate throughout our sleep cycle”

Conclusion 

During sleep, we heal both physically and emotionally. NREM sleep improves our memory and repair, restores and rejuvenates our body, builds muscles and bones, strengthens our immune system and cleanses our brain. REM sleep consolidates our memory, heals us through dreams and improves our mental activity. REM sleep is essential for brain development and NREM sleep is essential for brain maturation. As a whole, we sleep to heal holistically. 

Don’t wake someone from sleep unnecessarily, because their body is in recovery mode and waking them will definitely disturb their healing and overall health.

Reference

1. Patel AK, Reddy V, Shumway KR, et al. Physiology, Sleep Stages. [Updated 2024 Jan 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK526132/. 

2. Institute of Medicine (US) Committee on Sleep Medicine and Research; Colten HR, Altevogt BM, editors. Sleep Disorders and Sleep Deprivation: An Unmet Public Health Problem. Washington (DC): National Academies Press (US); 2006. 2, Sleep Physiology. Available from: https://www.ncbi.nlm.nih.gov/books/NBK19956/. 

3. Shrivastava, D., Jung, S., Saadat, M., Sirohi, R., & Crewson, K. (2014). How to interpret the results of a sleep study. Journal of Community Hospital Internal Medicine Perspectives, 4(5). https://doi.org/10.3402/jchimp.v4.24983.