I amdealing with arthritis, so it's important for me to get up and move around so I don't "freeze up." I use an online timer and set it for 30 minutes. When it goes off, I do a variety of things. Sometimes I get up and walk to the ladies' room - if there's a line (which there usually is) I do some posture exercises against the wall. Sometimes I'll use one of Spark's seated workouts - core, arm, cardio or even just a desk stretch. And sometimes I'll get up and do some leg strengthening exercises.
I also keep a 16 oz travel cup with me, which I refill on any of my walks to the ladies' room. I fill this 4 times a day so I get at LEAST 8 cups of water.