It's called hyponatremia. One of the reasons things like Gatorade were first developed. As I understand it, Gatorade got sold to one of the softdrink 'majors'. All I know is it got sweet - and I stopped using it.
I make my own now, a variation on traditional farmers' drink here in New England called 'haymakers punch' or 'switchell'. Those have a bit of molasses, which I don't use; it's just water, splash of cider vinegar, pinch of salt. Salt disassociates into sodium and chloride in water. Those aren't the only electrolytes lost - but they're the important short-term ones. I also take magnesium citrate in my daily 'stack'. IMO we're all magnesium defficient to varying degrees but it's released from our bones when serum level drop so it's not time sensitive.