When people do things they don't want to do, they easily feel tired. The psychological rejection of this matter further aggravated this situation. You probably don't like math, so you especially want to sleep in math class. The solution is simple, it depends on whether you are willing to do it or not. That is: be sure to preview in advance. When previewing, you don't just skim the tidbits, but you can't. Ask your classmates around you, or your teacher, or go home and ask your parents. In the meantime, you must feel very tired and want to sleep. However, once you are ready, you will feel relaxed as a whole. When the teacher is lecturing, you will have a * * * sound. "I have seen this, and I have seen this." Being sure of yourself will make you feel happy and you will never be sleepy again.