How to portray a character in his spiral into madness?

He starts seeing things that remind him of his guilt, like he'll be walking along happy or whatever and he'll see something and he'll take it as a sign. It will bother him more and more and then he starts to get thinner and thinner and cares less and less about regular life as nature keeps throwing it in his face in his downward spiral. His life starts falling apart. Eventually he gouges his eyes out or burns them with chemicals so his environment will no longer remind him. In the end, he finds God, peace and forgiveness, like he'll see himself as a child again or something.

I took the bleaching the eyes part from a movie I saw so that's cheating, but I've experienced this and before seeing the movie I even broke down once and said I would rather be deaf and blind because the world is a constant reminder.

A good movie to watch about a downward spiral from guilt or madness would be The Machinist and also the movie Pi. The bleaching the eyes one is from the movie Another Earth.

If you are using music I highly recommend sampling tracks from The Downward Spiral by Nine Inch Nails. The song Crystal Japan by David Bowie is another one worth listening to. The VHS recording version on Youtube is especially creepy. It inspired the Nine Inch Nails song ''A Warm Place''. Hurt by NIN and Johnny Cash are also good, as well as I Hung My Head by Johnny Cash. Two rap songs on the subject worth checking out are Shook Ones Pt II by Mobb Deep, and Mind Playing Tricks On Me by Getto Boys.