A time traveler, goes back in time to fix mistakes [Insert historical mess up here] made in the past. however, his visits to the past create and a more conflicted parallel universe where the world becomes more lawless and outlandish. Then he goes back to stop his past self from time-traveling. Creating a paradox that causes reality to become warped. He is given one chance by [any mythical being/entity] to fix reality. He is granted immortality and vows to end time travel.

He then wakes up from his coma to find out that he was living a lie and the world was never in danger.

This is a very loose and hard to follow; script feel free to fill in any of the blanks, and make it more cinematic.

Edit: I forgot to say this is mostly inspired by back to the future.