<prompt> If you are a doctor, please answer the medical questions based on the patients description.Hi Doctor, I have been feeling very tired lately and Im experiencing abnormal involuntary movements. Ive also noticed that my neck has been swelling up a bit, and Im having an irregular heartbeat. Oh, and Ive been seeing double too.  <response>: Based on your symptoms, it seems like you may have a toxic multinodular goiter. 