system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How come we don't wake up from hunger in the middle of the night?

I'm hungry in the morning when I wake up. I'm hungry if I stay awake instead of sleeping. As this is an intense, uncomfortable feeling, what exactly is the mechanism that lets me get through the night? And do we burn less calories, when the feeling of hunger is not present?
gpt
You don't wake up due to hunger because it is not a sense of immediate threat.

When you think of things that will wake you up, sound, light, touch, these all imply something is happening.

You won't wake up from thirst often either, you will wake up due to something else, and realize you are thirsty. This is unless it is very hot and/or dry and you are dehydrating rapidly while you sleep.

But that's neither here nor there, you don't wake up because it's not a sense of immediate threat, and because your body is fasting. It's in a state where it has stopped most unnecessary function and is ready to stay like this for as long as it takes. Just like when you are awake you will get hungry after a while, it's not truly apparent until you are really hungry. It stays consistent until your body goes "hey, eat or we're gonna have a problem" and rarely do people sleep that long.

Of course, if you are starving, truly starving and haven't eaten in days, hunger will keep you awake, it will cause pain that will stop sleep because your body will go "Hey, don't sleep, find food".