In summer '97 to spring '98, I was in a minor depressed state. What happened was, I somehow forgot how to be happy. Which is weird because nothing was going on to make me feel that way. I just did. And so I first tried to generate a feeling that feels good, and then see if I can hold on to it. The problem was, I kept thinking about it throughout the day to the point where it didn't feel good anymore and instead became annoying. And so I had to come up with another feel good feeling. And then I dwelled on that one too, and it became annoying also. Finally, after some time, I decided that I should stop concentrating so much on how I feel and just feel whatever and move on. And the result was that I slowly started to feel better. I wasn't dwelling as much as before but left it alone instead and went about my day. I didn't ignore how I felt though, I just didn't beat it to the ground to the point where I dug myself back into the hole like I use to. Of course the story doesn't end there, and there were times when some situation or another happened and made me feel down. But later just I got back up, Baruch Hashem.
I see a different form of this dwelling happening to other individuals as well. Sometimes someone finds something that s/he doesn't like and then keeps concentrating on it so much that s/he becomes really annoyed. -- I think that if something is bothering us, we should personally talk to someone like a friend who can help us examine what it is that's bothering us and then help us get past it. Once that's settled, we can be less negative and be more positive.