You have symptoms of Hashimoto's Disease which is a serious thyroid autoimmune condition. Your pounding pulse, muscle cramps and sweats are indicative of a thyroid storm. Without medication, you could die. Hashimoto's typically runs from hyper to hypo thryoid, and your doctor can order a scan to see how much/how little hormone your system is 'uptaking'. Hashimoto's thyroiditis or chronic lymphocytic thyroiditis is an autoimmune disease in which the thyroid gland is attacked by a variety of cell- and antibody-mediated immune processes. It takes several months to find the right level of thyroid hormone replacement (synthroid) and you should be having blood tests monthly, then bi-annually, and when levels are stable, once a year to make sure you are maintaining the proper level of thyroid hormone.