Is it possible to have hyper thyroid symptoms with "normal" test results? on synthroid (thyroxine) for years. sleep problems, anxiety, tachycardia, stomach issues

Yes: Get re tested soon by endocrinologist.

Sure: It is possible to have these symptoms even with normal lab values. It is also just as likely that these symptoms currently have nothing to do with your thyroid function and have a different cause altogether. Your primary care doctor and endocrinologist need to put their heads together and decide which it is and then go from there....You may need a sleep study, EKG, and/or other work-up