I weigh myself before a ride, take water before the ride, 24 to 48 oz during the ride, weigh again when returning and sip water after. I did not do this last year and was getting cramps and dehydration. I have found also that mixing my own chocolate milk after a ride in high heat will help restore and recover for the next day. I also freeze some cranberry juice in a 12 oz plastic bottle(bottom part only) and fill it before a ride, it stays nice and cold and slushy when i need it the most. My bp was about 90 over 68 after some rides and i was feeling a little light headed. Using the above with rest stops have helped keep me more normal.