Hi. I have written before, but I wonder if there are any ideas as to how to manage my situation. I have had a problem on and off with panic attacks, irregular and fast heart beats ever since I started on levothyroxine for an under active thyroid. In August I had really awful irregular beat episodes which would last nearly all day (helped a little by a beta blocker). On visiting the doctor he was insistent to up the beta blocker. I had to beg for a thyroid test (I had a normal one in the May). When the result came back my TSH was 9/t4 18. I upped my dose from 75mcg a day to 100mcg. After about 6 weeks the episodes stopped, retested at t4 18 and TSH 0.4. However the episodes started again mid Jan, restested at TSH 0.3 and t4 16. I clearly have a small window where the thyroxine is the right level. Does anyone else suffer like this? I have thought of asking for a monthly blood test just to monitor to see the range. But it constantly means visiting dr for forms etc. I am now back on 75mcg for a month, and then will try 75/100 alternate.