I do a lot of computer work, reading, close work. I find I, and my body feels a lot better if I take quick fitness breaks every hour. I have DVD's with 10 minute workouts, or I do stairs, or go walk around my building, anything just to get moving, warmed up and stretched out.
This helps keeps your metabolism burning, prevents you from getting stiff (important with a chronic disease) and generally makes you feel better! Our bodies were designed for moving, not sitting!!