When you're depressed life can be very bleak for a long time, and then it can be very empty.
Like right now I'm feeling low because I fucked it up with a Girl that I really liked. Not on purpose, I just suck at relationships or whatever.
I'm not suicidal or anything but you know those little half a tick thoughts of just blowing your brains out cans pop up? Almost like it would be a release. Usually your capable of brushing them away and being like "nah, things will get better. Things can always be better, that's not me. That's something else creeping in."
Sometimes you get brought down to a very dark abyss and you can't just will yourself out of it, you get stuck, and the longer your stuck the more your reality becomes the abyss nothing cancels out the negatives, then it's not so much as the emotional pain as it is the emptiness.
Anyway I was in that abyss for about 2 years myself, I imagine that there is no guarantee of not falling back in. I just remind myself that as long as I'm still Alive, I can fix things, that I can still fight, I can be better, that things can be changed.
You have to fill your heart with Courage on days that you've got nothing else.