How can you tell if you are depressed?

I used to be able to make myself snap out of it, but lately its getting harder and I dont have as much desire to do so. I just feel as if some tradgedy has happened and Ive lost something but I dont know what, I cant pinpoint it. I am meant to be starting a new job on tuesday but its going to take a LOT of effort and willpower to make it happen.....I feel I have lost patience with life and am no longer willing to try, even if it harms me.....its as if all I want to do is hide and have nothing bother me. I dont want to face reality at all and I feel insecure and like everything is boring. Maybe there is no way to make this situation pefect maybe I just need to do what I have to.....but surely its not normal to feel like this about life? What does everyone else feel?