Because you are not interested in what the teacher said, it sounds like a lullaby. At this time, all the cells in your brain are inactive, producing a substance that is easy to make people tired, and then you will feel sleepy; After class, the external environment disappeared and exciting things happened (chatting with classmates, playing small games, going out for a walk, etc.). ), so the brain is active and naturally awake.

I suggest you cultivate your interest in learning mathematics. You can read books, newspapers and so on. Thoughts on mathematics knowledge and keeping up with the teacher's class. When you can understand, you won't be sleepy. When you come up with a better solution than the teacher, you will feel very excited, hehe ~ ~