An excellent article from the Pryomaniacs on the subject of depression, from one who has suffered from it:

First and above all: you must see depression as your enemy, to be killed and buried and replaced. It is not your friend. It has come to feel comfortable and comforting, even friendly. Your real friends may not understand this, but I do. They see you wrapping a sopping-wet blanket around yourself, and think you’re nuts. But I do understand, more’s the pity. The sodden blanket is comforting because it’s familiar. It has assumed your body-temperature. It has sapped you of strength in the process, too, so that the thought of doing anything different simply seems like too much to ask.

…if you’re a Christian, you need to understand that Christ’s bequest to you is joy (John 15:11), and that God’s will for you is that you rejoice (Philippians 3:1; 4:4). You need to see, understand, and embrace — hear me, now — that right now, you have the very best reasons to be the very happiest that you could ever be.