This game really has legs, no pun intended! It's got great feeling controls and that Meatboy-esque "try, fail, instant reset, repeat" gameplay loop that's really addictive. The tutorial is really well-made, and the general aesthetic of the game is fun and a little silly in the best possible way.
It seems like the skill ceiling could be really high, I think speedruns of this game could be wild. That being said, in my opinion the skill floor is pretty high too; meaning, I haven't been able to finish either level yet after about half an hour. I think I'll echo what some of the other commenters have said, the sanity meter is a little strict. My suggestion though is this: the current meter is correct for an experienced player; after all, I'm assuming you are able to beat the stages as they are now. I think stages would benefit from having multiple difficulties, where easy might give you way more sanity to start with, and as you get better you can play higher difficulties.
Overall, I'm definitely excited to see where this project goes since you're planning to continue it.