Been exercising for a month, and feel like crap. I went to my doc for my PSA blood test, and other work ups. Two days latwer my doc calls and tells me my thyroid has almost complletely shut down. What caused this? been taking medicine to prevwent this for 10 yrs.A mix up in drug doses. My doc said its a wonder I had enough energy to even walk. Now it will take several months to get baxck to normal. No wonder that walk up those steep ramps was killing me. After 55 twice a year.