I've made a platformer with custom-physics before so I understand how difficult they can actually be so I totally get why the controls are rough.
Here's a few things that I noticed that would really help the game (you might already know this too):
1. Your character's jump is so high and so far for the tiny platforms. The platforms should be slightly larger and spaced out more to accommodate this.
2. Your character's acceleration is instant which is really difficult to get a handle on. They move so fast and they get to moving so fast so quick.
3. Your character will sometimes get stuck running in place when you switch directions too fast after landing.
4. The character's speed in air is way too slow, there's barely any control over it. This makes it feel like the character is "slipping" off of platforms because the speed on the ground vastly outdistances the speed in air.
As for the Sanity mechanic, I wasn't really a fan of it. It's an interesting concept and I totally get how you got there, but it's just frustrating in practice. All you're doing is punishing the player unnecessarily. It adheres to theme, but I feel the point of the theme is to find fun mechanics that are interesting by taking away control rather than just taking away control to make the game less fun to play.
I still had a good time and I think it's great that you managed to do so much in such a short time.
Your visuals are incredible and you put in so much effort in so many areas that weren't necessary. I can really see your passion for games.
Congratz on making a game for the jam!