Oh man, I was surprised how much you were able to creep me out with such simple visual elements. I think that means you spent time in the right places :)
Balancing the health/sanity/oxygen was a nice touch, and your stomach drops with dread a little when you dive further and the sanity leaks away. It's tuned nicely so you have just enough oxygen to reach the next cave.
What was the money in the top right for and how do I get more of it?