Too much salt (like too much of most things) can be deadly. In fact, you need to take only 1 gram of salt per kilogram of weight to die. This was often used as a method of ritual suicide amongst Chinese nobility-who were often the only people who could afford large amounts of salt.
However, too little salt poses the same danger. Salt is essential to the body and if you drink too much water, it can flush the salt out of your system and cause a fatal Hyponatremia. This is what killed a woman by the name of Jennifer Strange who entered a “hold your wee for a wii” competition.