TSH is not a good way to tell if you are actually hyper. You can have a low TSH and be hypothyroid (like me ). Please try and get your free T4 and T3 tested too. If those are also high, it suggests there is something going on. I doubt it's because you are suddenly needing less thyroid hormone. It might be that you are not using the thyroxine very well so it is building up in your blood, giving you hyper symptoms.
It would be a good idea to get the following checked as any of them could be responsible for your symptoms and changes in TSH.
serum iron (needs to be well in range)
ferritin (should be 70-90 for good health)
vitamin B12 (supplement if below 500, even though bottom of range is only 200)
Were you feeling "hyper" or were you just told you were from your TSH result? If you were well, then you probably weren't hyper. You just had an abnormal TSH result. Low TSH is very common in people who are on thyroid replacement hormones like thyroxine. There has been recent research that shows that TSH is pretty much useless for people with hypothyroidism (I know you were hyper before RAI but if your thyroid is pretty much destroyed you are essential hypo now).
I wonder if there is a possibility that you are actually going hyper. If that is the case, it sounds like you are now on too little thyroxine and it needs increasing. You really need to get your T4 and T3 tested though if your doctor is insistent on using blood test results to alter your dose.
I hope that helps a little.