Bring coffee to class. If you drink a cup of coffee in class, the effects will last about three to four hours. If you don't like coffee, drink a different caffeinated beverage, such as an energy drink.
Bring snacks that will give you energy. Instead of candy bars, bring a granola bar, whole wheat crackers or pieces of fruit. These foods are filled with healthy carbohydrates and can help you feel energized longer.
Moving your body will help you feel more alert in class. Moving around in class would distract others, so get a little exercise before class. Go for a brisk walk outside for 15 minutes, or do calisthenics in your living room.
If you're constantly tired in class, you might need a longer-term solution. Sleep eight to nine hours each night. If your schedule doesn't allow that, try napping 30 to 60 minutes every day.