Take a break from working already! I love doing a spinal twist at my desk because it really loosens up my lower back and gives my eyes a rest. I try to do this every half hour or so.
Push your chair slightly away from your desk and then sit down gazing forward. Bend your left knee and plant your foot on your chair - slip your shoes off if you're wearing heels. Reach your right arm up and cross your elbow over the outside of your left knee. You can increase the intensity of the twist by pulling with your hands and putting weight into your left foot.
Stay here for a few breaths or as long as you want. Then slowly release your torso back to center and place your left foot on the ground. Don't forget to do the other side! Twisting is so important for the health of our spines. This feels good and is so good for you. Try it right now and let me know what you think.