I've been on .175 levothyroxine for a very long time (like 2 years). Couple of weeks ago i started to have muscle pain in the chest and the back, i started having high anxiety, panic attacks, high pulse rate and palpitation. I ask my doctor for a blood test to check my TSH and Free t4 levels. I found out last week that i was in hyperthyroîdism so the doctor that checked my TSH and Free T4 level gave me a lower dosage (.150) How long before my anxiety drop and i go back to normal?.