If your thyroid is not really functioning too slowly, and you're taking synthroid, then you'll go hyperthyroid, and that will show up on the blood tests. Typical symptoms of being slightly hyperthyroid are (like you say) jitteriness, insomnia, and your heart beating faster than usual.

You will want to be tested to make sure you're not hyperthyroid, because they tell me that being hyperthyroid makes MG worse (though that may only be the case when you're hyperthyroid because of an autoimmune attack--I don't know). Also, being hyperthyroid over a long period of time will deplete your calcium and weaken your bones.

Abby