Researchers have found a possible link between obesity, a lack of physical activity and an increased incidence of developing fibromyalgia. The study further shows that a high BMI, being overweight or obese, is a strong and independent risk factor for future development of fibromyalgia.
My advice: Get out there and move your body. Whether it's squeezing in a walk with a friend or getting on the floor and doing some sit-ups - doing something (regardless of what it is) will help prevent chronic diseases and get you in the habit of moving your mass.
Source: Association between physical exercise, body mass index, and risk of fibromyalgia: Longitudinal data from the Norwegian Nord-Trøndelag Health Study