so dehydration IS bad for your BP. I can attest as I recently passed out during a long ride break (which I know better) because I did not hydrate before and during the ride. Still learning my new home state of AZ and while humidity is so low I was not feeling it like I did in TN LOL. When the EMTs showed up my BP was 90 over something. It was simply a dehydration event according to the ER doc.