Is it possible to have been misdiagnosed?!?

I've just been started on a small amount of medication for a 'mild' hypothyroidism. Am taking LETROX 50, 1pill a day. However, I can't seem to stop thinking that perhaps it might be a misdiagnosis or something. Is there a possibility of having been misdiagnosed? If that were to be the case - is it possible to get off the medication, and go back to normal? Or does the medication ruin your thyroids/glands system?????? what happens... is there such a chance?