ya exactly. You've heard of water poisoning before? Like that lady in the states who died after drinking all that water trying to win a wii? It's not too much water that causes death, but that all that water dilutes the electrolytes in the body until it reaches a level where the brain is unable to send electrical impulses as the medium is diluted enough to degrade transport. no efficient medium to transport electricity from the brain = organs shutting down.
Now, i'm not saying that if you watch your sodium intake you're going to die. thats sillly, but it's not the beast you hear about at times. it's a needed nutrient in the body and reaching the rda is a very smart idea. take a look at gatoraide, you know two of the contents of it are sodium and potassium. it contains them because those are 2 minerals lost through sweat and need to be replentished in order to maintain top CNS functions for sports. so even the odd day here and there where you go above or below is honestly no big deal.