I kind of know what you are talking about. I'm not clinical depressed, but sometimes feel this sadness. It feels like waves that strike you. I would like to think "If they're waves, let them go through you". One moment I could feel so low, but later I may feel better, just with some time and thinking...hopefully.

Where I come from, there is this fragment of a song. Actually, it's a poem used in a song. It translates, roughly, like this:

"The hole that stands in front of you has exactly your size.
I don't know if you're going to fall or not.
All I know is that love is tenacious and comes up again, like the sun"

I like to think of this "love" as "self-love". It may sound cheesy but, when you're down, just keep pushing up and you'll rise up again.