I think going off Seroquel could definitely cause weight loss on the order of 5-10 pounds per month, since I gained 5-10 pounds per month when I started it. So I wouldn't be surprised if it was the fact that you stopped taking Seroquel. Talk to your doctor or a nutritionist about gaining the weight back, and it would be a good idea to get a full body checkup by your doctor, since losing weight suddenly can be hard on your organs.