Somebody linked to my page from a Baidu search for "sleepers in class." This search linked them to my web long entry about classes of sleeper cars on trains. The reason the search linked to "sleeper class" because native English speakers don’t usually refer to people as being "sleepers," unless they are talking about spies.
As a language issue, a person who is physically sleeping is a "person who is asleep," or we would say, "he is sleeping." We see the person still as primarily being a person who happens at this moment to be sleeping. On the other hand, a person who was planted by a spy organization with the plan of being inactive for many years would be primarily viewed as an inactive spy. Colloquially we might refer to him as a "sleeper," since his condition is not temporary but rather characterizes his whole identity.
If one wants to do an English language search for pages about students who sleep in class, I suggest that a better search would be for the words "student," "asleep," and "classroom" or "in class". The word "teacher" could also be used to clarify the search parameters.