You don't have to feel way down to be depressed. I look back a year ago from now and realize I was depressed, although not as bad as I ended up a few months ago. I didn't "feel" depressed then, but I know now that I was. If sadness, dark thoughts, wanting to die, lower than normal energy, inability to concentrate, etc. persist, then I'd say you are depressed. If something just doesn't feel right, best to get checked out.