Pretty common for me as well. I take a water bottle into class these days and if I can get away with it a banana and a chocolate bar. Sugar and fruit is good if you need to pay attention. In my case, I think it mostly has to do with the horrible food they serve at University.
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Life is real ! Life is earnest!
And the grave is not its goal ;
Dust thou art, to dust returnest,
Was not spoken of the soul.