Casting spells takes energy so they aren't going to be particularly useful in re-energizing you.
Adequate sleep and a healthy diet are essential to maintaining normal levels of energy in the body. There are many things that can cause feelings of being tired and low energy levels. Lack of sleep, poor diet, stress, etc can all be part of the problem. In addition, you might want to have yourself checked by a doctor to make certain there isn't something physical going on.