My dog is taking Throzine for a thyroid disorder. What would the symptoms be for over medicating.

The thyroid was diagnosed first, a couple of weeks later she started having gm seizures. At least 1 & day, the most was 8 in a day. She went on 2 different meds for seizures. It cut down on the seizures but the side effects were horribly. This all happened about the same time.
The vet would test her blood to see if he needed to increase her thyroid meds. The blood test showed to increase meds. I read that the thyroid condition could have caused the seizures. In Dec 2007 I took her off the seizures meds (gradually) she was completely off them by the end of Feb. 2008. She hasn't had one since Dec. 2007. I read that the seizure meds cause a false reading in the thyroid test.
I'm thinking she's getting over medicated. She's always panting & can't get enough water, lazy, etc. What's the symptoms for over medication.