Graves and rai 12 years ago. 125mcg synthroid (thyroxine). all levels normal. 6 years ago tsh dropped to 0 and free t3 & t4 low normal. tsh won't increase?

How do you feel?: This is really the question to be asking. Whoever is managing you may feel a need to lower your dose slightly to see if TSH rises / protect you from osteoporosis later in life / practice defensive medicine, but I'd be most concerned with how you actually feel. If you don't recognize symptoms / signs of hypothyroidism / hyperthyroidism, perhaps doing what's working is best.