It could be bio-chemical --- I know some things that have helped me when I am depressed (not that I can always do these things as often and as quickly as I should) is physical activity (walking, hiking, bicycling, swimming, dancing to the radio where no one can see me) and casual social interactions (making small talk while in a park or store....going to an art/craft show (or whatever)---and music, especially live music in a small venue---
I think we can regain ourselves (at least for periods of time) by going through the motions even when we don't feel like it. Not easy.
What is your day to day life like? Do you live in a city or a rural area etc? Things you like (or used to like) to do....(there are also good articles on this site) How old are you? work? school? [don't answer any questions you don't want to]