Yep, it comes and goes, sometimes gets pretty deep. Jay's advice is good if you can find one that works for you. But, depression is also a part of everyone's life. It's the degree that's a problem with us, it can be hard to shake after a day or two. Most people can do that on their own.
We all have positive things in our lives as well. Some may seem to have an abundance, but I'd bet you can find at least one or two in your own.
N~