Hi Lisa,
Your doctor's advice is fairly typical when your ATD dose is too high and causes hypothyroidism (FT4 below the range). The idea of stopping meds for a few days is to give your levels a chance to rise into the normal range before resuming meds. It won't hurt anything that your already resumed meds.
After the first 6-8 weeks on meds, the dose usually needs to be reduced anyway, and the maintenance dose ranges from 2.5-10 mg daily. Your 5 mg dose may end up being slightly too low or slightly too high, but it's a good approximation of what you probably need. It's normal to experience symptoms of hyperthyroidism when your thyroid hormone levels suddenly change. Palpitations are generally considered harmless although they're annoying. Since palpitations can occur in both hypothyroidism and hyperthryoidism, it's difficult to say if they're from the med reduction or the hypothyroidism. I'd suspect the hypothyroidism since your thryoid levels were below range. You should start feeling better soon, and if the palpitations are bothersome you could ask your doctor about temporarily using a beta blocker to reduce symptoms. Unless your heart rate is low, this might help. Best, Elaine