Had overactive thyroid for a second time in 13 years so had radio iodine in Oct 2016 which has since made me underactive. Wasn't prescribed any meds until January due to no appointment given by consultant despite chasing. Went to own GP in jan as had terrrible brain fog, poor concentration and falling asleep all the time. Now on 100mcg levothyroxine. Feel better now except for weight gain which is driving me nuts!