Swollen fingers and hands may be a sign of hyponatremia, but other signs, such as confusion and vomiting, are more prominent than is swelling. Drinking too much water, particularly during a marathon or similar long, strenuous event, may cause your body's sodium to become so diluted that you become hyponatremic. Hyponatremia requires immediate medical attention. There's no proven way to prevent or reduce most exercise-related hand swelling.