Dr. Matt Walker

Remove cortisol from an organism, they will not do well.

Right.

Yes, it is.

And that's one of, I spoke about, and we'll come onto this perhaps when we speak about emotional and mental health, and when we are underslept, we shift over into a more sort of activated, sympathetic, agitated state of our nervous system.

That's one aspect of it.

But there's another aspect of the stress

response, which is, yes, you get elevated heart rate, you're more sympathetic, which is this activated state rather than parasympathetic.

But you also get, when you're sleep deprived, a greater release of the stress hormonal axis, which is called the HPA axis, which if you really want to go into detail, it's the hypothalamopathy.

pituitary adrenal axis, which is a fancy way of saying that it's a signal from your brain going down to release cortisol.

So when you go into deep sleep, not only do you shift over into the nice, quiet, rested, quiescent state of the nervous system, but you also get a dissipation in that stress-related axis and the release of cortisol.

Cortisol, however, seems to be also under the strict control of your circadian rhythm where it drops down at night.

And in fact, you have one of the steepest declines right at the moment when you're starting to get sleepy too, almost as though your brain and your body know we can't have cortisol even at sort of normative levels that you would have during the day.

because otherwise this person is just going to still be a little bit too wired.

I would say it's one of the things that I would advocate in terms of a good sleep optimized routine, and we can come on to that.

Even if you don't think you're necessarily someone who's sensitive to that.

Now, it turns out I am someone who is sensitive to that.

It can really quite trigger me, so I stay away from it.

We often see this...

with insomnia too, and we call it the tired but wired phenomenon.

And people will say to me, look, I am just so tired.