It's like a switch.
Sex usually dignifies the peak of the "Honeymoon period" in a relationship, I stress the word usually, every situation is different.
Once you peak, and you get over that period, you become more settled and open to criticising your spouse. Criticism sometimes leads to conflict.
Notice when you've just nabbed this girl, you're in your early stages, sometimes you may tend to bite your tongue and hold back on negativity? Once that gets thrown out the window, and you're more comfortable with each other, fighting becomes a natural way of venting.
It's healthy to have the right kinds of conflict, anything to stop people from repressing negative emotions has got to be good.
That's just one explination anyway, plenty of factors could be the cause.
