This was pure and simple catharsis - I drew this image a few years ago, when I was suffering from a really bad depression. Somehow it felt better drawing it, giving it a shape and a form I could see and understand.
For me, a clinical depression is like a gash at the heart. Once there's an open wound, any tiny little hardship, problem or bad news becomes a seed that can easily take root and grow until it blooms black and horrible and painful inside, and you can't get it out without ripping out pieces of your heart along with it.
Even when it fades and goes away, there'll still be little scars, only they're on the inside, so you can't see them.