system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: Why does involuntary breathing stop and become voluntary when we’re reminded it’s happening?
gpt
Your subconscious (brain stem) controls breathing normally. When you think about breathing, your voluntary part (Cortex) takes control of it because it thinks you're about to do something related to your breath. Maybe you need to take deep breaths, maybe you need to hold it, but thinking about it means you want to do something. So it takes control, now you can stop it or keep going. 

After some time of you doing nothing, the subconscious takes back control since the voluntary part is just doing rhythmic breathing. So it goes back to auto mode.