All of us have read one or more books that really disturbed us deep down to the extent that we get upset even thinking about them. I have restricted this query to fiction because factual events disturb us in all sorts of complicated reasons that often do not share common grounds and are therefore difficult to quantify. Bearing that in mind, which particular book disturbed you most of all? It does not matter if you liked or loathed the underlying story.
For me, it has to be Anthony Burgess' A Clockwork Orange, followed some distance behind by George Orwell's 1984.