Will,

The symptoms you describe sounds like hyponatriumia to me. You drank quite a bit of water. Hyponatriumia (low blood sodium) is often caused by a combination of sweating (you can sweat quite a bit on a cool, dry day and not notice it) and high water intake and no significant sodium intake. It sounds as if you had 2 out of 3. I have gotten hyponatriumia a number of times on long rides because I sweat profusely and if I am not careful to take in sodium (table salt), I get nausea and vomitting. As an aside, the electrolyte replacement drinks do not provide significant sodium replacement. Also another aside, I live in central Florida and very few cyclists ever have this problem. I understand that the symptoms of hyponatriumia are weakness, nausea, vomitting, disorientation (this is as far as I have gone) followed by convulsions and death.

Of coiurse, there are quite a few things that cause the symptoms you mentioned so it could have easily been something else.

Pat