Other factors are derived from the environment such as cold air due to overburdened as a result, sleepy. Teacher's teaching method and it has an interesting, if not teaching, it will be tedious.
The other factor that comes from the environment, such as cold air makes me feel more comfortable, resulting in sleepiness. Audio and teaching methods of professors teaching if it is not attractive, it will make it look dull.
The factors coming from the other is the environment such as air cooler to feel comfortable, resulting in a sleepy. The sound and teaching methods of teacher's teaching effect if not interesting, it will make the boring.