Operators and Things, a (supposed) first-person account of a schizophrenic who recovered from the condition and wrote about her experience. The second half of the book is where it really shines, since the author attempts to analyze her experience as a window into the inner workings of her cognition: how it broke down, what she experienced when it did, how it recovered itself, and what led to it. Since the author is anonymous, and talking about one's mind is very introspective, it's hard to take away real science from the book but I found it fascinating nonetheless. While I really dislike pseudoscientific explanations of brain functioning, after reading this I took up the idea that the conscious mind is more of a time-slice scheduler and message-passer than where the actual computation is done. So concentration is about controlling your unconscious indirectly, like training a puppy how to play fetch: you give it suggestions of what to do, and ignore it when it doesn't do that :).

I'm linking to the Amazon page, but IIRC the book is old enough to be in the public domain and there is a free text version somewhere.

http://www.amazon.com/Operators-Things-Inner-Life-Schizophre...