Sounds like dehydration/over heating. Last year DH and I set off on a 56 mile ride with two bottles of water each. It got to 95 that day (in late April). I remember stopping at a gas station around mile 40 miles for gatorade and eating a Luna Bar. The last 8 miles were miserable, in hind sight I probably should have a called a friend when we stopped at the store. I got home and was so hot I laid in bed with a cool towel on my face and felt as though I would vomit for about an hour. I have never felt so terrible. I had been drinking before I was thirsty and hydrating prior to riding.

My best suggestion is to ride in the morning or late evening. The late evenings here are quite bad for heat, so I would keep those rides short. Other than that, rest in shade when you can. This won't help with a TT though. I may try the water bottle/spritzer.