Rest two fingers of one hand under your lower lip. 

Place the heel of the other hand on your navel, with fingers pointing downwards.
Breathe deeply as you look at the floor. 

Moving only your eyes,  look gradually from the floor to the ceiling, then down again. 

Repeat this for three or more breaths, as you entire body and eyes relax.

 

               This stimulates the brain and relieves mental fatigue.  It also                helps to enhance your ability to focus on near objects.