michael crawford, who has schizoaffective disorder, describes what it's like to live inside his head, in "living with schizoaffective disorder" part i and part ii at kuro5hin.org.
it's an impressive bit of writing, mercilessly open.

his descriptions of depression are to the point, and come close to what mine was like for me.

the other day, i was asked what it was like for me to be depressed, and i realised i had trouble describing it, because it's been so long since the last very bad spell. it feels like my brain has erased some of the bad stuff from back then, memories of what it felt like. i can't say that i mind.
it was strange to realise, thinking about depression, that i'm very much not depressed at the moment, nowhere near it, in fact, and that this is a newthing™ and that it just happened, the feeling better.
sure, there have been these mountains of change for the better lately, but the happiness still caught me by surprise. it's still kinda startling, actually.

today is a strange day, mood wise, with a strange mindset and some sadness and worrying, - but i see it as just that, and am not scared, like i was for such a long time, that any bit of unhappiness might mark the return of the total loveless-ness depression has always been for me.
these days, love, deep, real human connection provides a protective layer for my soul, putting a cushion between me and the boundless despair that erased my personality for so long.

and i'm very thankful and happy about that.