What does it take to stay feeling good?

I feel good for about a week and then BAM! the depression hits again. And it's not just like, "oh I don't feel well." It's like, "damn I feel like fucking ripping my soul out and feeding it to demons." I never want to get out of bed. And there is no one to talk to unless you count talking to my dog, but I don't think he really cares to listen. I feel the downward spiral coming on.