In Questions and Answers I try (as a true ExpEx, Expert-by-Experience) to answer some of your questions, as brief as possible.
Question that was asked yesterday:
“Why do we isolate ourselves when we are depressed?”
Answer: In my view there are four main factors that can make us isolate ourselves when in a depression: (1) Broken Filtering, (2) Exhaustion, (3) Shame and (4) Alienation.
The first one means that during depression, all sensory impulses from the world around us can come in either too weak, or much too harsh and intense; in which case we tend to protect ourselves from total confusion by temporarily “shutting off”. For a description of this mechanism, see my post Broken Filtering.
The next two factors, exhaustion and shame, are more self-evident. Exhaustion can be caused either directly by depression itself, or by the lack of adequate sleep that sometimes comes with depression. We then isolate ourselves because we feel we don’t have any energy left to get in touch with others. As for shame, this of course has to do with the self-deprecation that is inherent to depression. I discussed this several times here; for an example see my post Shame.
The fourth factor is the feeling that we’re already isolated and alone anyway, that nobody understands us in our depression, so it won’t matter anymore: a kind of indifference together with a feeling of alienation. For a description that comes close to this effect, see my post Fleeing the Party.