If you are feeling fatigued, a really quick way to refresh your whole system is to create a silent giggle inside you. Just start giggling, first with your throat, then with your stomach, and then with your whole body.
Let your whole body bubble with the joy of this giggle. You will be amazed how much energy rises up inside you! Only thing, you must do it silently. If you start giggling loudly, you will release the energy. Let the giggle circulate inside you. Let it become uncontrollable! Your whole body will feel warm and rejuvenated. Once you feel brimful of the energy, if you want, you can laugh out loud and relieve yourself of the excess energy. After 10-12 cycles of breathing, you will find that the stress is gone, the tension is released!!