well,horror and dark animes you say?
Tenchi muyo GXP is also a trumatic experience, but that's not the case...
Firestorm had it's 'moments' as well, so if you're in for a lowered IQ level it's the thing for ya~!
Perfect blue: the mind bugging movie! stalkers, psychological issues and lot's of murderers...
100 stories: a kick ass anime! goes through japan folklore and makes you wanna throw up, for example. theres this part, when you see somewoman having a flashback of how she cut her sister's eyes out after she saw her having 'fun' with thier father... totally ass kick.
Narutaru: the misstreated anime, once you get past ep 2. people start dying in ugly ways, at ep 11 i was screaming at the screen: "don't do it! stop killing already!"