Once the diagnosis was final, and I was able to get my condition under control, my weight didn't return to normal. In fact, during one particularly bad period, I gained a pound a week for three months. At least that's my firm belief. The job I was in at that point was physically demanding, at least for a fibromyalgia patient, and also very mentally challenging. Part of this can be explained by changing lifestyles, but not eating habits.
Part is also a result of how stress affects each individual.
Part, according to some, is due to poor sleep patterns which inhibit the release of a growth hormone which helps with weight control. I found that I couldn't control my weight until I reached a point where I felt in control of my life. That also meant most stress had been replaced with acceptance of my new lifestyle. And, it meant that my sleep, with the help of a prescription, was close to normal patterns. I also found that I needed to seriously examine my dietary intake, and my exercise patterns, to determine the right balance of foods for weight maintenance.