“Brain Fatigue” and the Best Thing to Do on Practice Breaks

Other than putting our instruments down, what should we be doing during our practice breaks to mentally recharge our batteries and prepare ourselves best for the next chunk of practice?Watch cute animal videos? Take a quick nap? Grab some coffee? Is there such a thing as a "best" practice break activity? Maybe not, but there's some research in the creativity and stress-reduction domains which all point at one particular activity that could be worth experimenting with during your next practice...