In the book he says he chose the most prevalent to avoid meandering too much. His discussion of those disorders and the more general discussion of what is happening in the body when we sleep have helped me pinpoint some issues I have been having, even though I don't have a sleep disorder. I highly recommend it.
I recommend Meir Kryger's "The Mystery of Sleep." In the middle of the book, each chapter is devoted to a different sleep disorder (with accompanying anecdote).
It focused too much on these disorders for my taste, which might make it perfect for your taste.