I've been travelling a bunch recently. Jet lag is a funny beast. I used to let myself adjust slowly, returning east, but now I go cold turkey: Up at 7am every day, from the first day I get back. It makes sure I sleep through the night. Not making concessions to my body throws into relief what my body really wants to do.
When my body wants to go to sleep, the taste of sleep comes on. I get heavy and my head lolls.
During the period I would usually be fast asleep, I'm kinda okay, but it's like walking through treacle. I'm also cold.
Just before my body expects to be waking up - what is, local time, early afternoon - I get that taste in my mouth again, I feel super tired, and my bladder fills up. Give it another hour or so, as I come out of the slump, and my feet get really hot.
What's going on here? I've no idea. But I can guess.
First, my body helps me go to sleep. Even when I'm tired, I'm not necessarily sleepy (I hope you see the distinction). My body must be releasing something to make me sleepy. That lasts an hour or so, enough to knock me out.
That taste in my mouth? While I'm asleep, my body is doing its maintenance tasks. It's dumping out the nasty chemicals, metabolising stuff which it didn't during the day, taking the opportunity to check all my cells and digest the old ones, and whatever. The taste of sleep and crusty eyes, that's my body excreting through my face.
Second, when I'm waking up, that's my body doing its clean-up tasks from the overnight work. There's stuff it kept back because it couldn't excrete them earlier, so when it knows I'll be up and about soon, it flushes liquids to my bladder and the last batch of stuff to my mouth.
My temperature regulation goes to daytime mode last, usually just after I've woken up. My body heats up, and this is felt most in my feet which go cold/hot and clammy (I think this is because my body makes assumptions about whether I'm standing or lying down). I get this same thing if I stay in bed too long on weekends.
What this all feels like gives me a new theory.
I feel like I'm operating my body with levers and buttons, when I get up, I'm jet-lagged, and my body expects to be in deep sleep. I have to operate my legs with levers, and remember to reel my shoulders in, out of the way of door frames. Making breakfast isn't automatic, it's a sequence I have to assemble then follow: Get cereal, get bowl, open cereal, pour cereal into bowl, put down box...
This subjective sensation does not - does not one little bit - correspond with the idea that my body is resting.
What it corresponds with is lag. If I operate my body when it wants to be asleep, my body is thrashing to keep up. I'm overloading it. When I'm asleep, it's because my body is simply too loaded to sustain consciousness.
Those overnight maintenance tasks must be a dog to run. Saving my memory out to long-term storage, running over recent experiences to figure out what to pre-emptively put in the cache, monitoring cell division, allocating resources, doing integrity checks, figuring out how to digest the worst bits of that agro-industry food, shuttling chemicals round my body. That takes work! My body is a busy bee!
Consciousness - being awake - is what my body throws me as a sop when it doesn't need the resources for anything else.
(Apologies for the ugly mind/body division I've been making here. For mind, read 'the self-aware bit of the mind+body me' and for body read 'me.')