Sorry to hear what you are having to go through right now. Sounds like you are having a tough time. I hope you can get some medical help soon.
It's hard to say what will work since everyones disease is different. I've experienced some of what you went through, but probably no where near as severe. I've times when I'm flaring up that drinking anything is dangerous. Eating any food is a gamble as well. Sometimes finding the right schedule can help. Also, I've heard that eating at one time and drinking fluids at a different time can help. I guess the idea is that if you eat and don't drink, it keeps things a bit more sticky and solid, so they hang around longer.
I know that keeping hydrated, especially in the extreme heat, is very difficult. I used to have a job where I worked outside for long periods. Keeping enough water in my system was very difficult. Being able to drink anything, and not having it trigger violent BM's is sometimes difficult. Truth is your body needs water to function, and the symptoms you experienced with the racing heart and sweating sounds like you were in danger.
Sometimes getting the right foods in can help. Things like bananas, rice and dry toast can help reduce diarrhea. I personally found that fasting doesn't work for me since it just opens up the gut and allows anything I consume, food or liquid, to just shoot through faster. My disease runs from the diarrhea to blockage symptoms, and can change daily. I've found it very difficult, but possible, to find a balance, although staying there can be tricky. You may want to try some of the foods that traditionally stop things up as a possible solution. The other thing you can try are the water soluble fiber supplements that can sometimes slow down the transit times of foods.
I hope you find something. Sounds like you are having a very tough time.
"I'm just along for the ride."