I think you're thinking of
Flight of the Navigator.
It starts out with the boy playing frisbee with his dog at a dog show. Later at his house he goes out to find his dog then he sees something, falls into a ditch, and wakes up years later to find out that he was missing for a few years. He was actually picked up by an alien with a cool-looking ship and went to it's homeworld and came back, while 8 years went by on Earth.