I guess I could describe the feeling as; "too much information for my brain to handle." My first method to deal with this was to play on tiny, but to be frank the game just isn't that fun with only 4 civs. So I play on small now, but towards the later stages of the game, especially if I'm a warmongerer, it's just too much for me too handle. Between managing the cities, the civilian units, the fighting units, world congress, trading and everything else... It really makes it hard for me to finish a game, not because of strategy, but because there's so much to micro-manage.