Yes, the contrast dye could affect your thyroid.
Thyroid hormone is made out of iodine atoms. A blast of iodine (the contrast dye) could raise your thyroid hormone levels...or lower your thyroid hormone levels (if it saturated the gland).
Dx Graves 4/99, tx w/Tapazole & Atenolol - Remission 7/03; Relapse 1/06, back on Tapazole, remission & off meds again 11/06.
I absolutely refused to get the contrast when I went for my cat scan for that reason only. I didn't want to deal with a flush of iodine in my system. The good news is that it should wear off eventually and you'll be back to normal. Try to stay away from iodine in the meantime.