My theory behind my decision is that waking up the student seems to be threatening to the student. He would be embarrassed because of that. In addition, if he was sleepy, how can he pay attention to the lesson? One of my acquaintances is a teacher educator. He said that I should have woken up the student because it was my responsibility to teach him. Nonetheless, this student is over the age of 18--he is a young adult.
I do not agree with my acquaintance's remarks. I should not wake up any student who falls asleep in my class--unless it is causing distractions. However, if sleeping in class becomes a regular thing, then, I would talk to the student alone and try to work something out. For example, he is not like the student in the cartoon here. I never had seen him do it before. Thus, I think that it is due work overload, and I do not think that it would happen again.
image source: http://pro.corbis.com/images/42-16279700.jpg?size=572&uid={BB7C7CC9-181D-4176-8079-E5E79A640AB2}