Hi hurting! I don't have depression, but recentely it happened also to me to feel sad without a reason...in these cases it seams really difficult to find what could make you feel happier. In that occasion I came here to talk with some friends...as you made with this thread . It helped me...hope that it's the same for you. Bad moments pass .
If I can give you an advice, a thing that you can do when you happen to feel down it's to do something that you like but isn't tiring and doesn't require much concentration...for example going for a walk, watching a nice TV program or reading a book, or something else...also if you have to study or to do other things, it's worth taking a day to relax if you need.
But I don't know how often you happen this...if it happens very often maybe it's difficult to take a pause every time. I don't know if this post can help you ...but I hope so . Hugs