Going to class can be hard on days you don’t feel too well or are tired, but it is valuable to show up to class and absorb as much as you can. You are paying for this, so you might as well get your money’s worth.
Besides, you don’t want to miss an important lesson or a chance to learn something new. Showing up for each class will allow you to soak in as much as you can, as well as create a pattern of showing up and being reliable. This also establishes professionalism by attending class. You can’t skip work because you don’t feel like going so you might as well treat school in the same way.