For a first game, it has quite some good ideas !
I really like the atmosphere and your use of lighting it really conveys the tension of being lost in a dark place not knowing what could come after you, the breathing mechanics are quite an original idea and well implemented with the theme.
Just one small isue to point out, your game's window seems to be a bit cropped on the page for the HTML version.
Other than that it's a solid entry with some good ideas, i feel only lacking a bit of polish for the character movement which seems a bit too fast if i had to nitpick but it's not that big of a deal.
Well done :)