Yeah, this happens to me ALOT down at the gaming center, i go down, then i play cod4 on lan only, and i just rape, then about 1 and a half hours in i start to get shit, so i go and play a diff game, like c&c kanes wrath, i come back on, and start pwning ass
I find it is alot easier if you dont play a game for a while, then start playing it again.
E.g. When i started to play special force, i started good, then i got addicted to it, and then i started to suck, then my net went down for a real long time, i started to play again, and i didn't suck so bad..
Maybe this is just me, but i think you should try a diff game, then go back to css...