Sleep late, like watching movies late at night. Talk on the phone too long in the middle of the night and it worked till late will result in the brain to relax is insufficient. There headache, somnolence and therefore cause problems in the classroom.
Sleep late, such as movies late at night to talk over the phone too long during the night and work until late at night, the brain don"t get enough rest. Symptoms of drowsiness, headache, therefore, sleep in class.