MichaelG: I see a depression as mental and emotional loop with positive reinforcement feedback.

Predisposition is required for loop to be complete:

1. Brain, which is not trained to analyze/debug itself
2. tends to react unconsciously,
3. which means drawing conclusions without seeing the full picture,
4. which causes blaming entities unrelated to real problem,
5. which results in senseless waste of energy and time trying to fix the unfixable.

So the loop goes as follows:

1. Feel depression
2. Focus on depression
3. Try to fight with depression
4. Depression grows as as it consumes more of your time and energy.
5. Next iteration starting from step 1, but spiralling in intensity.

To break the loop, focus on productive things instead of depression.

Recognize that you ARE the master in your own mind and CAN change your train of thought in ONE moment.

Yes, it is that easy. I've been there and I know it's not just a theory.

Good luck :)