So been T3 only for 18 months. Feeling way better than when I took T4 but still sluggish/brain fog. Endo won't increase T3 from 40mcg/day because 'my TSH at 0.07 shows I am possibly overmedicated and my FT3 3.8 is within range (3.1-6.8) and FT3 measurements are very variable' (it was 3.4 6 months ago - that doesn't look very variable to me). What significance does TSH have? What are the dangers of it being 'too low'? I have no symptoms of overmedication only undermedication.