I have many bad habits, but there is one always makes me upset. I like nodding off in class. Nearly everyone will have this bad habit in summer.

I have many bad habits, but there is one always makes me upset. I like nodding off in class. Nearly everyone will have this bad habit in summer. But I will nod off in every class and every season. Usually, I will nod off when the class begins about ten minutes. I hate this. I have tried my best to correct it. But I failed in the end. This habit troubles me lot. 
我有很多的坏习惯，但有一个让我一直都很心烦。我喜欢在课堂上打瞌睡。在夏天几乎每个人都会有这种坏习惯。但是，一年四季每一堂课我都会在课堂上打瞌睡。通常，开始上课十分钟左右我就会打瞌睡了。我很讨厌这一点。我也曾努力改正过。但最后我还是失败了。这个习惯让我很心烦。