You might assume that waking easily when disturbed means your sleep isn’t very deep, or that it’s just poor quality overall.
But here’s the thing - sleep isn’t just one long stretch. It moves through different stages that repeat throughout the night, and each stage has its own job to do.
Take Light Sleep, for example. Even though you’re asleep, your body stays a little bit alert to the world around you. That’s why the tiniest noise can sometimes wake you.
So, could it be that people who are easily disturbed are just in Light Sleep? And if they were in Deep Sleep, would they sleep right through it?
What exactly are Light and Deep Sleep? What other stages are there? And what really decides your sleep quality?
What are the sleep stages?
Sleep is generally split into four stages: Light Sleep, Deep Sleep, REM (Rapid Eye Movement), and Awake.
Why it helps to know your sleep stages?
Because how these stages flow is a big deal when it comes to sleep quality. Understanding them, and keeping an eye on your own sleep patterns, can help you tweak your habits for a better night’s rest — something you can do more easily with a device like the CUDIS smart ring.
A handy way to do that is with the CUDIS smart ring app - Dashboard - Sleep.
A typical night usually has 4 -6 cycles, each around 90 minutes. The stages of sleep that matter most for recovery are Deep Sleep and REM. Light Sleep and Awake simply allow your body to ease into Deep Sleep and connect each cycle.
Deep Sleep
During the night, deep sleep, also known as SWS (Slow-Wave Sleep), is the one true luxury. This is when your body does most of its repair work and sorts out memories.
At this stage, you are pretty much unaware of anything else. Your muscles relax completely, and your breathing and heart rate slow down.
Around 70% of the total amount of GH (Growth Hormone) is secreted during deep sleep. This assists in repairing muscles, recovering physically of sports enthusiasts, and growing and developing in teenagers.
In addition to the benefits it offers your body as it recovers, deep sleep also cleanses the brain.
According to a 2019 study done by A. Fultz et al. in the journal Science, cerebrospinal fluid flows throughout your brain, clearing waste built up during the day. It isn’t surprising that “good sleep is key to feeling refreshed”.
Deep sleep primarily occurs during the first half of the night when it is difficult to wake you up.
REM
REM sleep is not too far detached from being awake. Right behind your eyelids, your eyes are darting back and forth, dreams are blooming, and your brain is sorting through memories and skills.
Although deep sleep emphasizes facts, learning to perform something is embodied in REM when you fine-tune a skill or hone in on a hobby. REM also helps with emotional balance coupled with creative thinking.
Although your brain is active during dreaming, your muscles actually become inactive, preventing you from acting out your dreams.
Light Sleep
Light sleep is the intermediary stage between wakefulness and entry into the deep sleep stage. It consists of two stages.
If you’ve woken up with a jerk, thinking you are falling, then you were most probably in light sleep stage 1.
It is widely accepted that stage 2 is the starting point of actual sleep. Sleep spindles and K-complexes keep you asleep while also maintaining alertness to the surroundings. They also start filtering out distractions and ease you gently into Deep Sleep.
During Light Sleep, it’s easy to be disturbed by noises. So if you're a sleeper who wakes easily by noises, it doesn't necessarily mean your sleep is poor — it might just mean you were in this lighter stage at that moment.
Note: This article focuses only on how different sleep stages may influence sensitivity to noise. It does not address cases where excessive light sleep is caused by factors such as aging, stress, medical conditions, or individual differences.
Awake
Brief awakenings at night are totally normal, especially if they’re short or you don’t remember them.
For most adults, the total time spent awake after falling asleep should stay under 40 minutes. If you wake up often and struggle to nod off again, it could mean your sleep cycles are being disrupted.
Typical adult sleep stage percentages
Normal adult sleep roughly breaks down like this:
50% Light
22% REM
23% Deep
5% Awake
For a 7-hour night :
50% Light - 3.5 hours 22% REM - about 1 hour 32 minutes 23% Deep - about 1 hour 37 minutes 5% Awake - 21 minutes
These numbers can vary with age, gender, and individual differences.
When sleep gets disrupted
Sleep disruptions throw these numbers off. People with insomnia often spend longer in Light Sleep and more time awake.
OSA (Obstructive Sleep Apnea) is another common disruption. Research in Nature Zhang et al. (2025) found that OSA patients have altered sleep structures, particularly in REM.
Factors affecting sleep
- Age - Deep Sleep drops as we get older, awake time increases.
- Stress & emotions - Stress can make falling asleep tricky and waking easier.
- Light & body clock - Blue light suppresses melatonin and shifts your sleep cycle.
- Diet & substances - Caffeine, alcohol, and nicotine all affect sleep.
- Exercise - Regular activity increases Deep Sleep; high-intensity exercises close to sleep can make falling asleep harder.
- Environment - Noise, light, or extreme temperatures disrupt continuity.
Tips for better sleep
- Keep a routine - wake up and go to bed at similar times, even on weekends.
- Try the 20-minute rule - if you’ve been awake in bed for over 20 minutes, get up and do something relaxing until you feel sleepy. This helps stop your brain from thinking the bed is just a place to be awake.
- Create a bedtime ritual - dim lights, step away from screens, read, take a warm bath, or stretch.
- Optimise your bedroom - keep it dark, quiet, and cool. Blackout curtains, earplugs, or white noise help.
- Watch meals and drinks - avoid heavy meals late, finish caffeine by 2pm, alcohol at least 3 hours before bed.
- Get daylight - morning and daytime light helps set your body clock.
- Track your sleep - wear a sleep tracking ring like CUDIS and check the CUDIS App to see your sleep stages, spot patterns, and improve your rest.
References
Fultz, N. E., Bonmassar, G., Setsompop, K., Stickgold, R. A., Rosen, B. R., Polimeni, J. R., & Lewis, L. D. (2019). Coupled electrophysiological, hemodynamic, and cerebrospinal fluid oscillations in human sleeping brain. Science, 366(6465), 628-631. DOI: 10.1126/science.aax5440
Zhang, P., Wang, L., Xue, J. et al. (2025). Sleep architecture characteristics in patients with acute ischemic stroke. Sci Rep 15, 16996. https://doi.org/10.1038/s41598-025-01619-6
