As a woman who is currently PMSing, shut your ignorant mouth. Until you've felt period cramps for three days straight, you have no right to complain about us.
Most dreams are caused by desire though i don't think you wanted to dream about this. It could have also been you saw someone or something that caught your attention and you projected it in your dream, you might have seen mail or a bus and when you where falling asleep you were unconsciously...