Hello all. I just wanted to mention that about 7 years ago I found a book that actually helped me change my thinking patterns enough that I was able to bring myself out of chronic depression. I'm now convinced that negative thinking really can change the mind's chemistry by constantly hitting our brain with the addictive drug/chemical adrenaline. We get so used to the slight jolt we get when we think negative or anxious thoughts, that we are unable to give them up. It's very similar to the well-known fact that meth users suffer from deep depression after using amphetamines over a long period of time.
The book that helped me learn to take control of my thoughts, so I could get off this destructive merry-go-round, was Psycho-pictography, by Vernon Howard. Don't let the slightly silly name fool you - this is one of the most powerful books I've ever read.