When I had fast heart rate and exhaustion, I was severely hypokalemic (low potassium). I needed an IV. You should NOT ignore this; you need to have a full blood work-up to determine if you have an electrolyte imbalance. Water alone is not going to fix the problem, and if potassium is the issue then no amount of salt or sugar will rectify it. At the very least, you should probably go to an urgent care or walk-in clinic.

Unfortunately the doctors where I live do not know anything about J Pouches. They didn't do urine analysis, didn't test my potassium, and just put a straight Saline IV in which helped for about an hour. I explained to them they I didn't have a colon and they looked at my like I had 2 heads because I also didn't have an ostomy. They gave me one bag of Saline and then sent me home and told me I needed to drink more water!

I think it's pouchitis again because I have been having complete water BMs so I am going to call my pouch specialist tomorrow.

While controlling the diarrhea is critical, you really only have two options with hydration: get enough fluid (however much that is) orally, or get it intravenously. I hope you are able to drink (and absorb) enough water to stay out of trouble. If you are truly dehydrated, vigorous exercise may turn out to be extremely risky. Exercise is generally good for you, but not if it requires IV hydration.