You know those commercials for anti-depressants that strive to make people realize that depression isn't just feeling down. They don't do a very good job portraying what it's like to live with the disease.
I've got a chemical imbalance in my brain - it causes my depression. I have always had it, and always will. Medicine makes me able to function, most of the time, but not always. I think I have Seasonal affective Disorder too.
Depression is not about feeling sad, or losing interest in things you used to enjoy,
and it's not about fatigue and pain. It's a constant struggle against the awareness of the futility of your life. Nothing I have done, or will ever do, will ever mean anything. Why should I force myself out of bed every day to go to a job that doesn't really matter? if I wasn't there someone else would be, Why should I bother to put hours of work into a piece of art, that only a few people will ever see and fewer still like it enough to want to see it again? No one likes my stuff enough to spend five bucks for a print, so why should I bother? Why should I write, (see the same reasons as above) even if I ever got published, 200 years from now my work will have been forgotten. My fatigue and pain are caused by the sheer effort it takes to keep up the appearance that I am normal, that I understand this unnatural way of live we've invented for ourselves, that I believe things are ever going to get better, for myself or anyone else, for everyone else, when all I really feel like doing is screaming and ripping the flesh from my bones to stop the pain, but I can't do that, I'll get locked up for my own good, and I'll loose what little I do have.
That's what depression is, for me at least.