Thanks for taking the time to play my game and leaving a comment.
I tried to reduce the scenarios where you could switch dimensions and end up stuck in terrain. However, as the ability to switch is at the player's discretion, I decided to just add a restart level option in case things went south, and tried to design short levels so that progress can be easily regained.
The issue with the waterfall is most likely related to the way I implemented the flowing currents. Being in the water continuously applies a force to the player, so the waterfall is most likely accelerating the player collider straight into the ground.