In more severe cases, the athlete lapses into unconsciousness, develops epileptic-like seizures and may stop breathing or suffer cardiac arrest. Fluid overload of the lungs may produce pulmonary edema that leads to shortness of breath and coughing up blood-stained sputum. In Ironman triathletes suffering from hyponatremia, I have observed gross swelling of the hands and forearms. By drinking too much fluid during very prolonged exercise. As a result they develop a progressive fluid overload.
Women are at much greater risk than men for reasons that no one yet understands.
Alternatively, it is clear that a big part of the problem is the inability of the athlete to excrete the excess fluid perhaps because of high levels of fluid-retaining hormones. It may be that woman have larger amounts of these hormones, the nature of which remain uncertain. You have to drink a lot for a long time to develop a fluid overload. If runners are drinking less than 1 liter per hour, they are unlikely to develop the condition. Since you need to keep drinking for 5 to 6 hours or more, only very slow marathon runners and ultradistance endurance athletes are at risk.