Hi,Thanks for all your help in the past. My tsh has gone through the roof to 18 so my GP has upped my Levo. to 150 micrograms and will do full bloods in January. Since seeing him I have suffered with the usual sore throat and headache but this last two days I suddenly go so very tired that I could drop.This comes on all of a sudden. I know an under-active thyroid causes tiredness and felling cold and I do have those symptoms but this new symptom is so sudden and lasts an hour or two. Anyone else suffering this?