I was like that for a long time. I think it was just a few years ago, actually. I p. much just secluded myself from everybody and put up a fake front when I was with my friends. It was odd, like there was no source of depression, yet it seemed like everything I did was meaningless. I skipped school a lot, and slept almost 14 hours a day. It could've been school, it could've been problems at home. I don't remember, and that's also what happens. I block out all my memories of being depressed, and bad things that have happened in the past. Luckily though, I've been out of that for a few years now.
The end result of depression is always the same, and it's that you'll eventually come out of it. There is no such thing as perma-depressed, not even for manic depressants or bipolar people. They may go through it more than the normal person, but it always clears up.