Sleep Cycles, Explained

And two ways we can work with them.

“So, next time you see someone sleeping, make believe you’re in a science fiction movie. And whisper, ‘The creature is regenerating itself.” — George Carlin

We spend a third of our lives asleep, without really knowing why it happens, or what it is.

Can you imagine spending a third of your life at work, without ever learning what your job was? You’d go into each day expecting its failure or success to be a total gamble, beyond your control.

Don’t treat your sleep like Russian roulette.

The science of sleep has made leaps and bounds over the last half a century. It’s made up some of my favourite neuroscience and psychology papers in the U.K.

I’m going to cut out the jargon, and share the good, essential stuff.

Let’s have a look at our brains on sleep — what’s happening, why it happens, and how we can use this to rest more deeply.

The Sleep Cycle

There are 3 distinct stages of dreamless sleep. (Stages 3 and 4 are sometimes separated, but bear a strong similarity.)

These 3 stages are easy to grasp, because they follow on from one another in a logical order. You can’t skip from Stage 1 to Stage 3, or vice-versa, without going through Stage 2. The higher the number, the deeper the sleep, the harder you are to wake up.

  • Stage 1 — Lightest sleep. You’re “drifting off”. You can be woken very easily by somebody saying your name, or a thunderstorm. Stage 1 is when hypnic jerks occur: those sudden, unexpected jerks of muscles when you open your eyes abruptly wondering what just happened. (While scary, hypnic jerks are common and harmless. Keeping a regular sleeping pattern reduces how often they occur.)
  • Stage 2 — Light sleep. This is still light, but you won’t bolt awake often. K complexes occur here: irregular sharp peaks in brain activity. They are linked to staying asleep despite distractions and enabling memory consolidation.
  • Stage 3 — Deep sleep. Ever have a nap, and you wake feeling groggy and disoriented? That’s deep sleep. It’s hard to wake you up from this. Brain activity continues its slow down at this stage, reaching the lowest levels it will in a normal lifespan. For this reason, it is also known as slow-wave sleep. There are points here when neural activity is almost completely silent: as in, very little is happening at all. The brain is conserving energy and resting. Muscles are relaxed, and growth hormones are released, repairing tissue.

So, to simplify: light sleep in 1, memories strengthened in 2, deep rest in 3. Where are the dreams?

REM sleep

The fourth and final stage of sleep, Rapid Eye Movement (REM), is where dreams occur. Dreams only happen in REM.

REM is uniquely bizarre in that, for the rest of sleep, our brain activity is slowed considerably. In REM, brain activity speeds up to waking levels. Serotonin is released at an incredible clip in the first second of REM — greater than waking levels — before dropping again. Blood flow is increased, along with oxygen intake. Muscles are paralysed, so the sleeper is unable to act out their dreams (in normal circumstances.) except for the eyelids, which flicker similarly to how we look around at a real scene while awake.

Dreams have been suggested to help us:

The truth is, we don’t know for certain why we dream — yet. Until then, enjoy the funky visuals.

A full cycle

Each night, you go up and down the stages of sleep repeatedly, like a staircase. A nice visualisation of this can be seen here.

A full sleep cycle means going through all five stages. This takes, on average, 90 minutes to occur. The sleep cycle duration increases over the course of a night, stretching out to spend less time in deep sleep, and longer in REM. So if you feel like you have more dreams in the morning — you’re right!

Staying healthy

To get the recommended 8 hours of sleep per night, you cover 5+ sleep cycles. Less than 6 hours sleep (or <4 cycles) per night, and you wake up noticeably groggy.

This is because the brain’s been interrupted mid-clean-up operation: consolidating memory and conserving energy. (Remember: even in waking leisure time, your brain is still “up” working for you, to process thoughts and sensations.) Sleep is a little like mental floss: it keeps your brain healthy and shiny. While missing it occasionally is okay, too much neglect will catch up with you.

Are caffeine/alcohol/pills okay?

Caffeine is a little like a shot of morphine to not feel an injury. It might make you temporarily faster, but it is no fit substitute for letting your brain recover. The priority when you feel continuously tired should be to look at your sleep quality, not your 3rd espresso. Beyond its side-effects and addictivity, though, it doesn’t do any harm. Just make sure to drink before noon!

Alcohol can get you to sleep faster, but it significantly disrupts the sleep cycle itself. Drunken sleep is of poorer quality. Particularly in the latter half of the night, you will experience lighter sleep than you would normally get, and are more likely to wake up tired. It also disrupts your circadian rhythm over time.

Sleeping pills are widely prescribed to between 40–70 million Americans. (In the U.K, Zolpidem/Ambien is used as a rare and temporary last resort for its dependency risk.) Pills are useful for temporary sleep disturbances, but shouldn’t be taken regularly. Either take sleeping pills for two to four weeks maximum, or a maximum of three nights weekly over longer periods. Consider switching to herbal sleeping supplements, which are milder without the same risks.

Should I monitor my sleep?

Reaching enough deep sleep per night is particularly important for rest. You’re recommended to get between 1–2 hours of this per night. This is hard to check unless monitored via an EEG in research. Increasingly we use sleep monitoring apps, such as Sleep Alarm, to try and track this at home.

Sleep monitoring apps are clever, but unnecessary, with caveats in their ability to monitor accurately. If you swear by them and they don’t keep you awake, go ahead! But the answer to “Did I get enough good sleep last night?” is simple: How do you feel during that day?

Well-rested, or tired? On the ball, or stumbling? The latter indicates you didn’t get enough.

2 Ways to Get Enough Good Sleep

Here are some two simple paths to good sleep hygiene, so you do wake up on the ball.

I won’t patronise you by saying “exercise each day” or “avoid screentime”. Both are lovely, and true, but obvious: and often hard to implement with full-time responsibilities. I hope these paths are instead both thorough and workable.

#1 Set your alarm based on 90-minute chunks.

  • All you need for this one is a) your current bed-time, b) a guesstimate of how long it takes you to fall asleep, and c) 7.5 hours — also known as 5 full sleep cycles.
  • This gives you the formula for the time you are most likely to wake from stage 1 easily, and wake up well-rested.
  • Bed-time + fall asleep time (hrs) + 7.5 = ideal wake-up time.
  • For example, it takes you forty-five minutes to fall asleep. You go to bed at 11 PM. 11 PM + 0.75hr + 7.5hrs = 7:15 ideal wake-up time.
  • You can also use this to find your ideal bed-time. Just count backwards from your wake-up time.
  • Stick to your chunks. Keep your bed-time and wake-up time consistent. When you do have to recalibrate — say, to be up earlier for the airport — reconfigure your chunks earlier, sticking to 90-minute adjustments, to find your new bed-time.
  • Some people’s average sleep cycles vary from 90 minutes: this is okay! Trust your gut instinct: if you realise you feel better waking up 15 minutes earlier, do so. The key is awareness of the sleep cycle pattern, and consistency in sticking to yours.

#2 Sort out your bedroom.

  • Invest in some good blackout curtains, particularly if you’re living in a well-lit / urban area. Artificial light is incredibly disruptive to sleep. Blackout curtains give you a natural, darker environment better suited to our biology. If you’re on a budget and there’s a chink of light that’s distracting you, just throw a towel or t-shirt over it. The darker your room, the better the sleep.
  • Having a room that is cool overall — between 60° to 67° F — while warm and cosy inside the bed, is most conducive to feeling sleepy.
  • The transition from an overhead light to darkness is jarring: for your sleep as well as your eyes. Try to use softer, ambient lighting — such as any lamps, side-lights, or fairy lights — for an hour before bed instead.
  • Avoiding screentime before bed is hard. How about a deal: if you’re picking up your phone after a set bed-time, make yourself stand up and sit or lie somewhere else for the duration of using it. Always make sure the Night Shift / red light setting is on, and if it isn’t an inbuilt setting, download an app/extension that does so.

I’m going to bed…

Let’s refresh first, sleepyhead.

  • There are four stages of sleep: Stage 1, Stage 2, Stage 3, and REM.
  • In sleep, our brain waves slow down from alpha (waking), through theta (stage 1/2), into delta in deep sleep (stage 3).
  • Sleep helps our brains consolidate learning and memories, and our bodies to heal. K complexes and sleep spindles are linked to this.
  • REM sleep is the only stage where dreaming occurs. In it, the brain becomes as active as waking levels, particularly in the visual cortex.
  • Sleep is very structured. We all go through all four stages of sleep several times per night, in ~90-minute chunks.
  • One natural way to improve our sleep is to set alarms/bed-times based upon the 90-minute sleep cycle.
  • Another is to set up a cool, dark bedroom environment, with soft lighting and minimal distractions.
  • Strive to follow good sleep hygiene practises.

If you’re interested in the funkier side of sleeping, AKA how to wake up in your dreams, learn about lucid dreaming here.

I hope this story gives you a good grasp on what the sleep cycle is, and how our brain activity alters throughout a night. As ever, comment if you have any personal experiences or questions, and I’d be happy to respond!

Take care, and rest well.

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