Sagging mood

I am so depressed these days that I can't manage to get up the muster to be very productive. I am overwhelmed by a sense of failure in nearly every area of my life. My self criticism is the loudest thought in my head. There has got to be some way to get back on track. With so much to be thankful for in my life, I am finding myself wallowing in everything that isn't right. I see the Facebook comments of my friends, all of whom seem so normal and happy. Why not me?