Yeah well the description in my first post is out of the DSM... I've read myself into it a bit and as far as I can describe... it's like the usual depression, with despair and stuff, but with reverse vegetative symptoms. E. g. instead of getting agitated, one is apathetic, instead of having insomnia, one sleeps too much....
Allegedly there is a gene which has been linked to serotonin levels in the brain, it has been linked to AvPD, AsPD and Binge Eating Disorder. Since atypical depression is a lot about binge eating, maybe this is relevant here too.
Now that I got some info on Atypical Depression it really terrifies me. It's chronical and the usual onset is in adolescence. That fits me. I got depressed when ten, been dxed with "normal" depression when 14, and am now am 18. Atypical depression has been my life for 8 years now. It's devastating. I'm considering to see a doc again, which I have been refusing since my last therapy experience... maybe I'll try meds for it this time, too.