i don't think there is anything wrong with getting into the game you're playing, while you're playing it. get happy get mad these are the reasons why we play games. if we didn't have some small emotional connection to them they wouldn't be as fun. it would be like talking on the phone all monotone.
if you get upset about the game i think its best to quit out and chill yourself down instead of continuing to play. #1 you're just gonna play worse from being mad, #2 that is gonna make you even more upset. #3 you'll continue to be upset even outside of the game.
so if you get really upset, then quit out and come to the forums or get something to eat and take a break. or just stop playing for the day and move onto other activities because what you don't want to do is stay upset while you're outside of the game...then you might be treading on bad territory