I used to sleep in my English class a lot during my senior year of high school. It was my last period, and I didn't have enough energy to be able to pay attention to the teacher at all. I usually sat in the back, so the teacher didn't notice that I was sleeping. Well, maybe she did, but she probably never bothered to wake me up. xD
Most of the time, I don't daydream. I'm quite happy about that though, because daydreams usually distract me and keep me away from getting my work done. I still would've been able to get things finished even if I daydreamed (I think), but it probably would have just taken me a longer time.