Eli5: How come when you are relaxed or falling asleep you don’t need to breathe as much?

Question

Just something I’ve been wondering…

In: 1

Answer 1

For one thing you literally need less oxygen (and you produce less CO2) since a lot of processes like digestion are slowed and your muscles are less active. For another, when you fall asleep, your brain lets you accumulate more CO2 in your blood which means you don’t have to breathe quite as much.

Answer 2

Additional to your movement and bodily functions, your brain also uses a lot of energy.
when you are falling asleep all those processes are slowed and thus you need less oxygen.