Mechanisms of a Healthy Sleep

There are two major processes that regulate sleep:

  1. your sleep drive

  2. your biological clock.

  • These work together so that optimal sleep happens when the sleep drive is high and the alerting signal from your clock is low.

  • The likelihood that we will fall asleep is determined by the net effect of these two factors.

Biological clock.  Picture from

Biological clock. Picture from

When experiencing insomnia, sleep can feel out of your control. It can seem unpredictable, sporadic, or unrefreshing.

Well, what can you do?

The first step is to get an understanding of the biological and environmental mechanisms that govern our sleep-wake processes.

Sleep Drive (Process S)

Your homeostatic sleep drive, or process S, acts as your sleepiness fuel gage, telling you when you’ve had enough to function well during the day or when you need to fill up.

Graph representing Process S.  Picture from

Graph representing Process S. Picture from

  • As the day continues, your need for sleep steadily increases. Your sleep homeostat keeps running tabs on how much sleep you’ve used and will let you know when it’s time to put away that last email or cocktail and get to sleep.

  • The need for sleep is at its highest when your eyes are drooping and all that’s running through your mind is “I’m so sleepy.” If you have ever stayed up late or pulled an all-nighter, that feeling of extreme sleepiness is your homeostatic sleep drive demanding that you get some sleep.

  • Once you finally get enough rest, your need for sleep returns to its lowest point and your ‘tank’ is full again.

But how does our sleep homeostat work? What is the biological mechanism behind it?

The most consistent chemical proxy for our sleep drive is associated with the accumulation of adenosine, which is part of adenosine triphosphate (ATP), or the molecular structure of stored energy.

  • When we actively use our brains during the day and extract energy for ATP, the byproduct of this use, adenosine, accumulates faster than our brains can get rid of it.

  • As the levels of adenosine continue to rise, they begin to block the alerting signals in our brain that are keeping us alert during the day, thus making us feel sleepier.

  • Once we fall asleep at night, our brains require less energy, so the rate of adenosine accumulation slows down. This period of rest then allows the enzymes that scrub adenosine from our brains to quickly break it down so we can wake up in the morning without feeling too groggy.

Circadian Rhythms (Process C)

Our bodies naturally produce an alerting signal that keeps us active and functioning during the day. This is known as the circadian clock, or process C.

Graph representing Process C.  Picture from

Graph representing Process C. Picture from

  • This process is governed by the suprachiasmatic nucleus (SCN), your internal master clock, and closely mirrors the rhythm of the homeostatic sleep drive. The SCN is located just behind your eyes and is most sensitive to light and dark cues.

The influence of light on behaviour via the SCN.  Picture from

The influence of light on behaviour via the SCN. Picture from

When activated by light in the morning, it activates alerting pathways in your brain to help you wake you up.

  • It then dips slightly at mid-day, reaches a peak right before bedtime, drops sharply to help you fall asleep, continues to drop to help you stay asleep, and then begins to rise again a few hours before you wake up.

As adults, we generally feel sleepiest in the early morning between 1:00 am and 4:00 am and then again in the early afternoon between 1:00 pm to 3:00 pm.

  • The post-lunch drowsiness is actually a natural dip in our circadian pulse and not solely the product of boring meetings.

  • Conversely, we often feel the most alert shortly after awakening and again just before bedtime between 6:00 pm to 9:00 pm.

  • The evening burst is usually followed by a quick drop in energy, which makes it ideal for falling asleep if we time it correctly.

  • Our ability to sleep during the night and feel alert during the day works best when we are able to sync these two processes together.

Dynamic between Process S and Process C.  Picture from

Dynamic between Process S and Process C. Picture from

Arousal System (Process W)

Besides Process S and Process C, there is a third system that affects your sleep-wake rhythms: the Arousal System, or Process W.

  • It is also commonly referred to as the “warning system” or “worry system” because it is activated in response to danger.

  • At its core, Process W is an emergency warning system to help you survive in the face of danger.

E.G. If the fire alarm goes off in the middle of the night, Process W will jolt you awake so you can get to safety no matter how sleepy you feel.

  • Once the danger has subsided, this system will give way to your parasympathetic system, the rest and relaxation system, and allow you to get back to sleep.

  • However, chronic stressors can keep Process W perpetually elevated, making it harder to fall asleep or stay asleep. For most people in high stress industries and occupations, regularly practicing intentional relaxation strategies will be an integral aspect of successful sleep therapy outcomes.


Having gained a good understanding of the mechanisms of a healthy sleep, here are 3 tips to try out yourselves the next time you want to achieve a healthy nights sleep…

  1. …expose yourself to bright light in the morning.

  2. …avoid bright light in the evenings to help manage your circadian rhythms.

  3. …reduce irregular naps.

Click here to read our next blog that discusses the effects of sleep loss in more detail, and provides another 3 useful tips you can use yourself to help improve your sleep.

Umer Nawaz