Mark's Haddon's characters

I just read Mark Haddon's second novel, A Spot of Bother, in one sitting. I was struck again by how successfully he describes the internal life of a character with a unique medical condition as well as that person's interactions with his/her family. In this book it's depression; in his first book, The Curious Incident of the Dog in the Night Time, it is autism. I feel as if I understand depression much better than I did before reading this book.