As I understand it, hyponatremia is not necessarily too much water: its too little salt. Can be caused by excessive flushing with water, but can also just be electrolyte depletion through sweating and balanced water intake, no?
I had the same experience with hiking poles BTW, and found the swelling was also alleviated by lightening up on the pack, loosening straps and removing pack for rest stops: the circulatory thing
