Very cool game with an interesting idea! The fact that you take air pressure into account for the oxygen consumption is also an interesting touch which I did not think about! :)
I had a bit of a fight with the controls at first but after I noticed that you don't really need to use spacebar and shift it went a lot better. (Pressing the spacebar and shift stopped the movement in other directions for me). *I was playing the WebGL build.
You did a very good job, keep up the good work! :)
(How did you manage to get fullscreen to work on itch.io properly if I may ask?😅I wasn't able to get it to work myself).