Hans Fallada - "The Drinker"

To summarise this book, its about a middle class, middle age, middle of the road man, who turns to drink as his business and marriage start to stagnate. Through his own twisted perceptions and some of the twisted perceptions of society, his (relatively) innocent, and stupid, drinking habit becomes the basis for him being committed, for life, to an insane asylum, without possibility of release.  He loses everything, his wife, his home, business, position, and finally his own sense of himself - he becomes, as he says, a shadow.

And to add to it, this was written by a famous German author, who, before the war, had written best sellers and been feted as a success.  But this was written, in secret and in code, in the dark days of 1944, from inside a Nazi insane asylum himself.

Sounds like fun, but somehow, despite the obvious parallels with himself, he writes with amazing humour about the fall into disrepute, and the actions for which you would normally expect him to be so ashamed and try to hide, he blasts openly.  Even the point where he drunkenly tries to raid the family silverware to raise money for more alcohol, is discovered by his wife and nearly murders her (leading to his arrest and imprisonment in the asylum) appears amusing and lighthearted...

It is only when, later in the book, after he has recounted how he managed to fall from his respected position one glass of schnapps at a time, that he enters the asylum, that the tone becomes darker.  From this point you realise that the autobiographical nature of the story is getting so close to the bone that he cannot raise himself to joke about it, even in the blackest irony.  The pace and delivery change, to a more clinical, efficient description of his surroundings, the habits and lunacies of those he is locked up with and the inhuman treatment these receive.  In fact, the outside part, recording his fall, is written in a sort of warm glow - like that he describes he feels with alcohol.  You don't mind that he's tried to kill his wife when he's drunk, because its humorous, the actions don't carry any weight, any responsibility.  Its only when he sobers up in prison that the tone changes, to the cold, clear analysis of his situation.
It becomes an anguished tale of how the mental patients are forgotten and left to rot, a burden on the relatives and the state, who all wish the problem would just disappear (which the Nazi seemed to brutally solve).  But the character does not finish the story rotting as an unjustifiably locked up innocent... from his friendly beginnings you quite like him, and as he sobers up, you pity the harsh treatment, but by the very end, you realise he is not all there, that is 'incurable'... its just what has made him that way that should be changed.