I only get depressed when I'm being indecisive. Am I being indecisive right now? I don't know.
On a more or most serious note, my genuine regards and loving respect goes out to those people who are (or feel strongly) depressed. I don't want to trivialize it, because for some of us, it can be a long-term and debilitating condition. When I feel melancholy (albeit not depressed), I choose to reflect on how fortunate I am to be living in the here and now, versus some other time or desperate place. I'm glad that I'm not one of those people, who as Bono notes prior to MOS, inhabit our little blue planet and "are barely hanging on".
As the desiderata says, "strive to be positive", and if possible, seek to do something positive for someone else. And if you're really curious and have some time on your hands, then read "Choice Theory" by Dr. William Glasser. It helped me cope through a difficult time when I was far from home, grappling with doubt and a stranger even to myself. Another eloquent and helpful short-read is "The Turn of the Tide" by Arthur Gordon.
I know - far too much information here. Keep as positive as you can, and all the best to everyone.