Dr. Matt Walker

By about 4 a.m.

or 5 a.m., you're miserable.

Why?

Because you've now been awake, let's say, for almost 20 hours straight.

So you've got all of this excess sleepiness, adenosine, pushing you down, screaming at you.

You've been awake for 20 hours.

And your circadian rhythm is at its lowest point, desperately wanting to pull you into this thing called sleep.

And you feel terrible.

But then something strange happens.

By 11 o'clock in the morning...

relative to let's say, you've now been awake for many more hours still.

So you've built up even more adenosine.

So the prediction would be that if it's just adenosine alone that makes the difference, you should feel even worse at 11 a.m.

You don't, you feel better despite being awake for longer.

Why?

Because your circadian rhythm has come to the rescue and it's now starting its upswing and it lessens the distance between those two and you feel a little bit more alert.

But then as I push through later into the day by about 6 p.m., 7 p.m., you're now on your circadian downswing once again, and you've been awake for even longer.

And at that point, there's almost nothing that can keep you awake.

You're gonna be falling asleep on your feet and you're toast.

But that's a nice demonstration of how you can separate those two.