Being depressed isn't all about being sad, it's about you thinking people hating or disliking you because of all the small things you do.
You keep thinking, what the hell did I do wrong? And all in all you keep feeling judged, you become way more mentally sensitive which could suddenly leave you crying over a girl who you really liked for the first time since you had your last real crush, after you gave up on love, but she didn't feel the same about you as you did for her.
You start to forget lots and lots of stuff, you don't seem to care anymore about anything.. At all.. Yeah, you care about the few people that still love you.
But other than that? Nah. You're just waiting for the depression to blow over and then come back after a few weeks, days, months or years.