I spent a year studying in university in Japan, taking engineering classes with regular students. The number of people sleeping in class was sometimes impressive - in the worst instance I remember it was about a third of the class (but thankfully, usually a lot less). The professor just ignored them and kept going.

The real shock for me was when I went back to Canada and realized I'd picked up the habit inadvertently! I would naturally fall asleep in some boring classes and had a lot of difficulty stopping that. Generally the prof would notice and call me out to everyone's amusement, or a neighbor would give me a nudge. It really did not feel acceptable to sleep in class as in Japan.