You take a few hits on the water bottle every 10 minutes during a ride? Also, perhaps after that stop, you went at it too hard to soon. Your body probably thought you were done for the day and was in recovery mode, then you told it to start working hard again. It rebelled.

If you haven't been doing rides that long in this hot a weather this season, then that may be a big piece along with all the other pieces people mention to you.