Sci-fi short story ID


waiting for a time
A man realises that he's waking up to the same day everyday (a la Groundhog Day), finally works out how to escape from his situation, only to find he's been minaturised and the world is a creation of an alien race who have saved him. The specifics are not totally clear - either he's small, or the aliens are very big, and the reasons why he has been in a loop and broken out of it I can't remember.

Anyone know the author and title? I read it when I was much younger and I've totally forgotten it.