Why are you tired?

4min reading
Why are you tired?

We’ve already seen that our sleep is partly regulated by our biological clock. But there’s a second mechanism that makes us drowsy. It is the homeostatic process, or for you and me, “sleep pressure“. It’s this process that makes you feel tired and some fatigue at the end of the day and makes you want to go to bed.

Slowly but surely, the sleep pressure increases… 

The homeostatic process determines this urge to sleep. It varies depending on how you long you’ve been awake and how much energy you’ve used during the day. The longer we’re awake, the more the urge to go to sleep builds.

 biological clock

It needs to be at a certain level in order for you to fall asleep. A lot of insomniacs forget this. They try to go to sleep earlier in the hope that they’ll finally get to sleep that way… However, as they’re not tired enough, they fidget and struggle to fall asleep. Sleep doctors often encourage insomniacs to push back their bedtime, even if they end up having a really short night’s sleep. How come? So that the urge to sleep builds and they get used to the feeling. That helps to create fatigue. And hopefully manage it differently next time.

As well as helping you fall asleep with different sleep techniques and get deeper sleep with audio stimulations, the Dreem headband gives you personalized advice so that you can adjust your habits and daily routine according to your sleep needs.

But how does this increasing “sleep pressure” work? This is where it gets interesting. The homeostatic process makes you feel drowsy through the accumulation of hypnogenic substances in your body (from “hypno” we get to sleep and from “gene” generating).

The longer you stay awake, the more these hypnogenic substances accumulate in your body and make you feel sleepy. Adenosine is the name of the main hypnogenic substance.

So what exactly is happening on the cellular level?

 ATP (Adenosine Triphosphate) molecule, the universal energy source for all cells
First of all, remember this. All living things have a certain molecule which has an important role in transporting and providing the necessary energy to all our different cells(muscular, neuronal etc).

This molecule is called ATP (Adenosine Triphosphate). To give energy to our cells, the molecule needs to go through a type of “decaying” process. It is a complex phenomenon that we’ll save for another time. After this “decaying” process, ATP transforms into, you guessed it, adenosine (the principal hypnogenic substance, remember).



You know where this is going. As the day goes on, the more your body uses energy, the more the ATP “decays”… the more adenosine is created. And this continues to build throughout the day.

Adenosine likes to fix itself onto the neurons that are responsible for you waking up and prevent them from doing so. And it works the other way around too, it fixes onto the “sleep” neurons and activates them.


During the day, the gathering of adenosine in the brain will fiercely “put to sleep” the neurons that keep us awake and inversely, stimulate those who make us fall asleep! From a certain level, the drowsy effect is hard to fight.

A little digression about tea and coffee

Adenosine has a few natural enemies which fight against its effect and slow down you falling asleep and your feeling of fatigue. This is the case for caffeine in coffee and theophylline in tea. Their molecules have very similar structures to adenosine and they steal the place of adenosine on the neuronal receptors. And therefore stop the adenosine from fixing itself there and doing its work (and as a consequence, making us fall asleep).

But how do we wake up then?

During sleep phases where the brain is less active, that’s to say mainly during sleep, adenosine is turned into ATP. Every night, the adenosine level drops again.

The neurons responsible for waking you up, gradually freed by the adenosine and its inhibiting effect, gradually reactivate and help you wake up. In the same way, “evening” neurons stop being stimulated. This, in combination with our biological clock starts to wake us up naturally.

 Sleep pressure

The urge to go to sleep increases whilst we’re awake and decreases during sleep. It depends on how long you’ve been awake and how much energy you’ve used. The biological clock follows much less varied genetic and environmental patterns.
Have to wake up at a particular time? You’re probably not waking up naturally or at the right time for your body. The Dreem headband wakes you up at the best moment, regarding your sleep phases, for a calm and refreshed start to your day.

Find out more about Dreem here!


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