Just remember if you are in a depression that you have always, always come to the end of it, and that life returns to being worthwhile, enjoyable, meaningful, fun, and joyful.
One method I have used, whether "up" or "down" is to recite a positive "mantra". A Mantra is a sound, phrase, or words that are repeated over and over and over. Positive thoughts can conquer any mood you are in, provided you work to think the positive thoughts.
Here's a mantra that I'm currently using, you can make up your own to fit who you are or want to become:
I'm the possibility of joy, joy, joy, joy
I'm the possibility of fun, fun, fun
I'm the possibility of Creativity
I'm the possibility of Transformation
I've turned it into a little song, and sing it whenever I'm walking, or doing something like mopping the floor. Anything that doesn't take much mental concentration gives me a chance to think or sing these positive thoughts.
What are YOU the possibility of?