Why do some students sleep during class hours?

Most of the students sleep during class hours because they feel tired. I think many students in school would not be have enough time to rest.And another reason is that the class is so boring that make students want to sleeping. The teacher must pay more attend to the content of a lesson and try to make more interesting thing in the class. i used to sleep both in tuitions and school especially during chemistry hours he he....
students sleep during class also because they spend a lot of time at night in playing computer games in internet cafes and in their homes. A lot of students today have their computers at home and they become addicted to playing anime and heavy computer games, they sleep very late at night.most students get tired because of their extra-curricular activities and so they drop asleep. others do so because the teacher is too boring to bear. sometimes it is because of the lesson. lack of rest is also another reason. worst reason is that they lost interest in schooling.
sometimes prof. acts like a sleeping pills so what can students do ? also if the topic which prof is teaching may not be of our area of interest. but i prefer to sleep in room rather than class.
But many students sleep during their afternoon session only na?So itz better to start classes early and finish it in afternoon.happy to see your response...