About 8 months ago, my doctor checked my thyroid levels because I complained of hair loss/breakage, dry skin, low heart rate (even while exercising), colder than everyone else, inability to lose weight on a diet, etc. My thyroid levels came back as hyper rather than hypo. I was sent to an endocronologist who conducted several more blood tests, ultrasound, and the iodine uptake test over a period of 4 months or so and they all came as hyperthyroid and with no goiter, Grave's disease. My father had this at about the same age as I, 30 and I was advised it could be hereditary. Although my father had all the symptoms and to an extreme. His eyes bulged, he sweated profusely, severe weight loss, his heart beat was rapid and strong, and he couldn't stop shaking. He was treated with radioactive therapy and no takes synthroid. I, on the other hand, have had none of these symptoms. In December, my endo gave me a low dose prescription to start taking to bring my thyroid levels in check. I refuse to take the medicine at the moment, because I'm not sure what I'm treating. I have no symptoms, and I'm not sure why I would take medication to treat symptoms that I don't have and certainly aren't bothering me. But in the past 2 months I have had 2 instances where after running for 2 hours or so that I almost pass out. Both were when I stopped in a store after my run, and once standing I felt like I would pass out, I had to go outside, take all my layers off and sit down on the sidewalk to keep from passing out. Could this possibly be because of my hyperthyroid? Should I start the medicine even though the endo agrees that I have no symptoms? I am very concerned about weight gain with the medicine, since I am actively trying to lose weight.