Too much Vit C can make you more prone to kidney stones. That's the worst outcome I've heard of

This has happened in extremely rare cases. It reveals how essential proprioception is for everyday movement. After losing his propioception Ian was completely immobilized and had to painstakingly relearn how to move by consciously tensing muscle groups. To this day every movement he makes requires complete focus and visual contact with each part he is trying to move. Basically he bootstrapped a worse form of proprioception via vision.

https://blog.oup.com/2016/06/movement-without-touch-ian-waterman/

He was interviewed on a radiolab episode which is where I heard of him: https://radiolab.org/episodes/91524-where-am-i I especially like the story of how he once saw a pretty girl and the split second of erotic mental imagery caused him to collapse on the ground 🤣