I rode an organized century in northern Illinois yesterday. By the finish the temperature had reached 100 degrees with very high humidity. In the course of the ride I estimate that I drank 14+ bottles of water / water with NUNN / Gatorade, but I simply could not absorb enough water and was somewhat dehydrated at the end. While just short having the of chills, I did mild nausea, bloated feeling, and had stopped sweating about the time I rolled in. If the route had been ten miles longer, I would have had to stop to cool off. As it was, I felt kind of hung over for the rest of the day and this morning. A hundred mile ride is usually no big thing, but this one took it out of me.

Milkbaby is right; even with electrolytes, your body can absorb only so much water, and shed only so much heat. At some point, you simply must throttle back.