I'm with Hooligan. I have a chemical imbalance that results in me being depressed for no particular reason. So do tons of people on this site. If someone has bipolar disorder or major depressive disorder or just a case a "clinical depression," depression can exist -- even severe depression - - with no trigger per se.

If you have a chemical imbalance you may benefit from medication. You may want to consider seeing a psychiatrist, and a counselor/therapist to help you deal with your depression. Best of luck.