To fall asleep, core body temperature must drop, which is facilitated by warming the outer surface of the skin to radiate heat.

“for you to drop your core body temperature the opposite has to happen which is that you have to warm up to cool down to fall asleep and I mean warm up in a very specific way you have to have the outer surface of your brain warm up you have to get blood to the surface of your skin and that surface is almost acts like a snake charmer that it Dr draws the warm blood from the core and it pushes it to the surface and you radiate the heat out and as you radiate the heat out said your core body temperature plummets”

“the body's sort of vasoactive capacity for Distributing that blood and then releasing that trapped heat from the core of the body is superior when you are lying down and therefore your body temperature can drop more quickly which is one of the many reasons why it's not as easy to fall asleep when you're sort of at a 45° angle and why the quality of your sleep won't be as good”

“in part it's because the warmth of the room is starting to make the sort of face a little bit more Rosy it's drawing the blood out to the surface so what's happening the core of your brain and your body temperature are starting to drop and at that point that's why you're going to start to feel a little bit more sleepy”

“the way that your body does this is by pushing blood out to the surface regions of your skin notably your hands and your feet because these are these highly vascular regions and you had a great podcast from one of my heroes and good friend Craig hel who's done some amazing work on this at Stanford so naturally as we lie down blood races to our hands and our feet and also our head and we start to release that heat trapped in the core of our body and by releasing that heat at the surface our core body temperature drops”

“it seems to be temperature that when your body is recumbent lying flat horizontal the distribution of how your body is able to move blood around the different regions and decrease your core body temperature meaning it can push blood warm blood out of the core of your body to these surface areas and when you push it out to the surface areas you release that heat it's this huge thermal dissipation that happens when we move Blood Out Of The Core to the surface you emit that heat and your core body temperature plummets when your body temperature your core body temperature decreases”

“by lying down the body's what we call vasoactive ability to distribute that blood in a way that is permissive for thermal dissipation of core body temperature is superior and that's the reason why we find it easier to fall asleep lying down than let's say semi-recumbent or certainly propped all the way up”

“when your body is recumbent lying flat horizontal the distribution of how your body is able to move blood around the different regions and decrease your core body temperature meaning it can push blood warm blood out of the core of your body to these surface areas and when you push it out to the surface areas you release that heat it's this huge thermal dissipation that happens when we move Blood Out Of The Core to the surface you emit that heat and your core body temperature plummets”