My father, well aged, began feeling terrible in 2018. Took him to the local ER. Hyponatremia. He told his older sister (the eldest sister had passed on a few years before this, so he couldn't run this past her), and his sister said she'd been on salt pills for years. Five years later, back to the ER. As the nurse was hooking my very ill dad up, I began to relay his recent history, including his diagnosis years earlier of hyponatremia. A couple of hours later, after blood extraction, bingo...hyponatremia. Two months ago, dad began falling. Compression fracture in his spine. He's 94 now. Back to the ER. I was on a cruise with the missus. Learned that they determined he was low on sodium....hyponatremia. AGAIN!!!

Some people dump electrolytes. I know someone who dumps so much magnesium that he has to drink two liters of his own concoction each day! I have gone to have cardioversions for my atrial fibrillation and the blood panel shows hypokalemia (low potassium). I eat plenty each day, from 1/2 cup of peanut butter, to coconut milk, to beets, potatoes,....lots of potassium each day. But they fed me two large horse pills to get my potassium back up.

All this to say that you may have to think of a wide variety of probably/potential causes of what you are experiencing.