There will likely be moments, long dismal moments, when everything seems empty, when all possibility seems to have vanished, and when your deepest desire is to simply vanish. The feeling, if it is truly profound, is one of hollowness. It is worse than melancholy. It is the essence of powerlessness, and this is the feeling inspired by true, clinical, depression. This is the backbone of suicide, and people can be brought to it by long hours of self criticism, blame, hunger, cold, and sadness.
If you get to this terrible country, first, do nothing. You think that the feeling will persist forever. It won't. It can't. Before you know it you get an idea, and that gets you thinking about something else, and then you think of something you'd like to try. Oh, you may sink back into the empty spot, but the worst part about being there is the feeling that it will go on forever. Once you know it goes away, it gets a little easier to take.
When the hours ache and linger, when the mind is poisoned with hurt, when the night is very cold and very dark, and when you can think of no where to turn, do nothing. Change will come.
Until it does, take a hot shower, and use some deodorant. Depression causes us to release all kinds of stinky pheromones.