My mom had an overactive thyroid at one point. All her life she'd had borderline underactive and the docs never treated her with the weight struggles that go along with that. She refused point blank to go and see the doc when she started losing weight without even trying. I lived a few hundred miles away, so while I recognized her symptoms and knew what was happening, I couldn't make her go and she was determined to enjoy eating all sorts of 'bad' food and still lose weight. I think when she did go to the doc she weighed 88lb, which was a bit of a difference to her normal 140.