I’m sorry you’re getting such insufficient sleep at night that you’re falling asleep in class. I think your concern should be more about missing the most crucial hours of your BC education than about your professor’s attitudes, which could be any mix of annoyance, disregard, or concern. I do recommend apologizing to your professor & explaining the reason. I know one college teacher who had been annoyed about a sleeping student until he found out the student was working a full-time night job to pay tuition. If your reasons are less noble, maybe don’t mention them, but commit to changing habits so you can stay awake.