I went through about eight months of the same hideous feeling you describe -- like you say, not major depression, but an inability to think clearly or feel happiness about one's achievements or to take pleasure in any of the things that I used to enjoy.

In my case, my doctor suggested it could be seasonal affective disorder and to a) wait for spring; b) try to get more exercise; c) try St. John's Wort if I really wanted to (though that was my suggestion and he didn't seem overly convinced it would help). He also offered talk therapy as a matter of course, but we both agreed that I didn't really need that. (There was nothing wrong that I could see with my circumstances, or my family life, or anything else I could think of that would justify that.)

Anyway, after much flailing and despair (and fruitless taking of St. John's Wort), what finally helped was... taking a B-complex vitamin every day. And when I say "helped", I mean, "lifted me out of the Slough of Despond and made me feel like my old self in under five days". I wondered if it could really be the vitamins or whether it was just coincidence, until I forgot them when I went on holiday for a week and by Thursday of that week I was in tears over nothing whatsoever.

So apparently my body was severely B-vitamin deprived for some reason. But I would never have guessed it would affect me so severely as that, or in that particular way.

All that being said, hello! I picked you off a list of LJ users who have Catherine Fisher in their interests, because I loved INCARCERON and now SAPPHIQUE with a mad passion. (Oh, all right, I loved Jared/Claudia with a mad passion. Whatever.) And I had seen you around before (probably on sartorias's LJ?), and thought that anyone who takes their user name from one of my favorite books of all time clearly has wonderful literary taste. :)