I go upstairs to a quiet room and lay on the floor with my eyes closed and I just do corpose pose. I think about the floor supporting my body and just letting go and not contracting any muscles. I only think about my breathing and letting my body become very heavy. After about 5 minutes I really start to relax and then all of a sudden I feel really energized.
I think this is a great way to let go of any stress or tension and it helps me focus when I feel exhausted too.