There are generally two reasons for being sleepy in class: 1. You are really not interested in this subject. You are sleepy because you didn't have a good rest.

If you are sleepy because you don't have a good rest, I think you know what to do, needless to say.

The key is interest. I like math very much. The more I listen, the more excited I am. ...

A netizen said that it is best to stand up and listen to the class. Indeed, if the teacher allows, you'd better stand up.

Of course, there are other ways, such as drinking a refreshing drink before class, preferably coffee. Drinking other drinks is harmful to your health. ...

There are not many effective ways to think. I think you'd better ask the teacher for advice and stand in class when you want to sleep. Don't tell me you should be tired of standing.