Mary,
I’m just curious – did you have a baby recently? It sounds like it could be Postpartum Thyroiditis if it is coming down like that on its own and the scan reading in the normal range.
Did your Endo say “Graves” for sure or has he mentioned thyroiditis?
Taking PTU during a cold won’t hurt – when I was first diagnosed I had a terrible cold and taking it was just fine.
BTW, you might want to get your progesterone and estrogen levels checked. Low progesterone can cause very similar symptoms to hyperthyroidism. (I had that, too, once I got it straightened out even things on the thyroid front improved).
Hope you are feeling better very soon!
Glynis