Worst I ever experienced was a 90+ degree day with me riding about 30 miles from home with only two water bottles and a 1.5L hydration pack, and no place to get anything to drink. I ended up stopping at a liquor store which was out in the middle of nowhere and asked them if they had anything nonalcoholic to drink. They said that their license doesn't allow them to sell non-alcoholic drinks. So I opted to buy a bag of ice with which I filled my water bottles and hydration pack, then sucked on some of the leftovers while I rested. On my way back home, about 3-4 miles from home, I started experiencing severe leg cramps. I stopped to try to walk them off, but a lady mowing her lawn at the house I stopped near came to check on me, and then flagged down a passing pickup to give me a ride home. I was grateful for the ride, though I did want to finish the ride myself, but realized I likely wouldn't have been able to.

The end result of that experience was that it taught me a very important lesson about not taking just water along for long rides in the heat, I needed electrolytes, too. So from then on I tend to take some kind of electrolytes with me, whether it be Gatorade mix powder, or if possible stop somewhere and get a Power Aid or Gatorade. On that ride I realized all the water I was drinking was washing all the electrolytes out of my system and I wasn't replenishing them. I was sweating so much and it was drying so quickly that I had crusty salt deposits on the side of my head from evaporating sweat.