Rewind Status Effect

Rewind would be a status effect that undoes your movement, healing, taking damage, and hunger bar (how much it's undone is based on how long you have the effect). However, it wouldn't undo things in your inventory, so you can't use it to repair your weapons and tools, retrieve or duplicate blocks and items, etc. It would be ended early if you move, heal, take damage, or (of course) drink milk (this is all from things aside from your rewinding).

I'm not sure how exactly you would get it, but I'm thinking a potion so you can easily prompt it to happen.

Imagine you accidentally fall into a deep, dark pit. You barely survive, and you're surrounded by hostile mobs. Just drink a rewind potion and fly back up to the surface with full health. Awesome, right?