In Breathing Underwater, Nick titles his January 10th entry "In my worst nightmares." Why does he do this?

Nick Andreas has been sentenced by the court to attend Family Violence Class. He's there because he physically assaulted his girlfriend, Caitlyn, replicating the violent behavior of his father towards him. To Nick, the whole experience of attending this group is a nightmare; he feels like he doesn't belong there. He's a good-looking, popular student from a well-to-do, respectable family. What on earth would someone like him be doing in such a class?
We can see from Nick's self-pity that he's still in denial over his violent behavior. At this early stage in the program, he tries to minimize what happened when he hit Caitlyn. He maintains that their relationship was "damn near perfect" and that he simply lost it that one time. Other members of the group are not convinced, however, and confront Nick about his behavior. This merely adds to Nick's discomfort, making him feel like he's breathing underwater.