在上课睡觉的英文表达方式是 "fall asleep in class" 或 "nod off in class"。

"Fall asleep" 是一个常见的说法，意思是睡着，常用于讲述某人在某个场合或某个时间内睡着的情况。"Nod off" 是一个俚语，意思是打盹，常用于讲述某人在做某件事时不经意间打了个盹。

下面是一些例句：

I couldn't help but fall asleep in class today. I was up late studying for my exams. (我今天上课忍不住睡着了。我昨晚熬夜复习。)
I was so bored in my history class that I nodded off. (我在历史课上如此无聊，以至于打了个盹。)
My math teacher always talks so slowly that I fall asleep in his class. (我的数学老师说话总是如此缓慢，以至于我在他的课上睡着了。)