@ Kilimbo
There's another way of looking at it. If you look at the book after it's over there are picture that made me think of the following:
He was falling in one direction the whole time! There were two cities with "space" between them. he was from one city, but in the other... his gravity was fixed to the other city, so he 'fell' all the way back to his city... he was in the other city to give them a special drug that they did not have yet.
(I know, I have a very 'original' imagination...)