The doctors may be right about the potassium and magnesium, but it's hard for us to say, since we don't know your situation. Magnesium deficiency is common among those of us with thyroid conditions.
Did you have parathyroid(s) removed at the same time your thyroid was removed? Parathyroids control movement of calcium and it's common to have calcium issues following their removal.
Did your doctor tell you to take supplements to keep your levels up and/or eat foods that are rich in calcium, magnesium and potassium in order to avoid deficiency again? These are electrolytes and must be kept in balance with other electrolytes - sodium and chloride.
Many of us have to take magnesium supplements to prevent symptoms of deficiency. Magnesium citrate seems to be the best type to take, as magnesium oxide is mostly good as a laxative. Care must be taken not to let potassium get either too high or too low as they're dangerous, either way.
Your doctor should test you periodically, to make sure you maintain adequate levels of all three of these nutrients so they stay in balance. You should talk to him to be sure that's in future plans as you shouldn't have to live in fear.
I did not have any parathyroids removed... currently on tums 4 times daily and my doctors seem to be arguing over whether or not to keep my calcitriol.25 twice a day ir keep it doubled which they did when i was taken back to hospital... my levels were all in normal limits 5 days after initial drop in mag pot and calcium I just am scared they are going to get low again or do reverse and get too high... my docs cant agree I went to a big hospital to get best care and now they are just acting like they have no real idea what to do ... my endocrinologist is on vaca and she managed to message me once saying she would stay on lower dose of calcitriol and change tums to a tablet of 1000 calcium 4 times a day and if i wanted to add magnesium and potassium... so hard to know ehat to do when your doctors can't figure it out
Your endo must not know a lot about calcium... the body can't absorb more than 600 mg at one time, so taking 1000 mg 4 times/day is a total waste.
Did they figure out why your levels went down so low? None of them should have had a lot to do with thyroidectomy, since you didn't have parathyroids removed. If your levels are in normal ranges now, what's the point in taking mega doses of anything and taking a chance on getting them way too high? It would seem that taking normal daily doses of each of the minerals would be sufficient, with regular testing to make sure your levels are staying withing the normal ranges.
There may be reasons I don't know about, so this isn't medical advice; I'm just wondering why mega doses would be called for instead of maintenance dosages, once levels are in normal ranges.