Gabriel: As you've described, this kind of spiritual depression often goes hand-in-hand with the medical illness of depression or anxiety disorder. It just feels so much worse because we all look to our faith as something strong to lean on when we are going through tough times. I hope you don't mind me sharing, but 15 years ago right after I was christmated, I started having severe panic attacks that started suddenly one night when I was saying Evening prayers. I developed depression and I had a huge crisis of faith and it began to erode my belief in God - the usual "do I really believe in God" stuff.
I always attributed this episode partly to job stress, buying a house and getting chrismated all in a period of 4 months, but it's got to be partly the attack of Satan on my new faith. It was a bad experience to go to church on Sunday and sing "we have found the True Faith" and have a panic attack just being there. Exercise, refocusing, mental health counselling, and some good drugs helped alot, but the one person I could always count on was my priest. He always told me and I still hang on to his words-"Lack of faith is not doubt, it's indifference."
Over the years I've realized that for converts, the high of the conversion experience may fade, but what replaces it is steadiness. I still have doubts and periods of spiritual doldrums, but I keep plugging on with my faith because I don't know of anything else in this world that is worth this kind of fight. God bless you and give you peace.