Can spending too much time on the computer make you dumb?

I spend a whole lot of my time on the computer. I do this because I make music (using my computer), I search and apply for jobs (using my computer), and I play video games (using, you guessed it...my computer). Lately I've been feeling "sick in the head". It's sort of like a mind freeze, or a brain haze, if you will, that happens mostly after playing a video game I am addicted to called UT. It started to happen recently, a few days ago. I will be feeling fine and then when I start playing the game for more than say, 15 minutes I will start to hurt in the head. It's making me feel dumb, like I literally can't think straight. I am starting to wonder if spending all of your time in front of a pc screen (not just playing games) can have a negative effect on the mind. Anyone think the same or know about this?