Is the point here to find the right answers to make oneself less unhappy? Sometimes that seems the whole point of therapy/philosophy/religion...but math and science, I don't think so.
If depression is self-centered then happiness seems...narcissistic, as well.
I think it is good to research various survivors and listen to what they have to say. To be wounded and depressed is no less meaningful than anything else.
Sadness and depression are stigmatized. I don't wholly agree that the depressed state is more selfish than other states...and, in fact, it has been my experience that those with the greatest luck and good fortune seem the most self-absorbed, while not even realizing it. They also seem to generally lack empathy.
If depression becomes self-centered perhaps it is because one so often has to keep it hidden and secret. It hurts to always have to hide a wounded heart.