I remember reading somewhere - I think it was an essay on Kafka in Anthony Storr's book Churchill's Black Dog - that Kafka's life, habits and central themes in his writing had led to a posthumous 'diagnosis' of Schizoid Personality Disorder. Apparently, he could be quite warm and companionable, but struggled with friendships and intimate relationships (though he had several). He was also consumed with the idea that people found him to be awkward and ugly - though the opposite, apparently, was the case. The characters in his fiction are trapped, confused, full of guilt, frustrated, and lacking understanding of the world they live in. I think there's a different form of diagnosis that he might also be considered as worthy of having!
I've just started reading Metamorphosis and Other Stories. The famous title story is about a traveling salesman, Gregor Samsa, who awakes one day to find that he has turned into a giant insect. Notwithstanding this drastic transformation, he seems more concerned with the fact that he's missed his train to work and will be letting both his employers and his family down (he's working mainly to pay off his family's debts). The story then goes on to detail the change this brings about to his life, and the attitudes demonstrated towards him by his family: kind at first, then increasingly cruel and negligent. He becomes a burden to them. It says a lot to me about societal conditioning, and to general attitudes towards disability, or 'difference' of some kind.
The beginning of another story, Investigations of a Dog, also says so much. You could almost imagine it as a post-diagnosis internal dialogue:
How my life has changed, and yet how unchanged it has remained at bottom! When I think back and recall the time when I was still a member of the canine community, sharing in all its preoccupations, a dog among dogs, I find on closer examination that from the very beginning I sense some discrepancy, some little maladjustment, causing a slight feeling of discomfort which not even the most decorous public functions could eliminate; more, that sometimes, no, not sometimes, but very often, the mere look of some fellow-dog of my own circle that I was fond of, the mere look of him, as if I had just caught it for the first time, would fill me with helpless embarrassment and fear, even with despair. I tried to quiet my apprehensions as best I could; friends, to whom I divulged them, helped me; more peaceful times came - times, it is true, in which these sudden surprises were not lacking, but in which they were accepted with more philosophy, fitted into my life with more philosophy, inducing a certain melancholy and lethargy, it may be, but nevertheless allowing me to carry on as a somewhat cold, reserved, shy and calculating, but, all things considered, normal enough dog.
That sums it up pretty well for me, anyway.
Interesting reading...