Excellent update, Flechas`s ideas seems to be similar to what are suggested at this forum, but of course he has some more weight to it.
Nodules gone, great!
About the anxiety / panic attacks; this is one of the long list of symptoms of hypo thyroid. So my guess is that when you quit the iodine, the hypo thyroid accelerated. http://www.calmclinic.com/anxiety/causes/hypothyroidism