Do you drink while you are riding? Or was your stop at the 1/2 way point the first time you drank? If it was 95 degrees, you should be sipping sports drink with electrolytes every few minutes and drinking about 20 ozs every hour (I drink about 32 ozs every hour).

I also drink a bottle of sports drink about 45 minutes before I take off. I have found that if I start out early in the morning after only having maybe a cup of coffee or tea, I dehydrate very quickly in the first hour.