I've overdone it a few times. Once was up in Wichita Falls in August where they have the Hotter than Hell 100 (I only did the 50 mile ride) bike ride. And once riding 40 or so miles with my Son In Law. Think it was the last time he rode a bike. I broke him. At the end on the way back in the car I was seeing spots. Not enough hydration. Sometimes it is just hard to get enough liquid to compensate for sweating. I'm a lot more careful now days but my mountain/hybrid bike only has room for one water bottle. Nearly all mountain bikers wear a water backpack like this.
I used to have one but it died and my road bike can carry two bottles so it was enough. But now I'm both riding the hybrid bike AND am a little older with a smaller margin of error so I bought the pack. It should be here today and I'll load it up for a ride tomorrow. One thing it does that a water bottle does not is put the water tube close to your mouth and easy to get so continuous hydration is more of a reality. I'll be testing it tomorrow. It means I can carry three liters of water with me. One on the bike and two in the pack. The one on the bike will typically have Gator Aid kind of stuff in it and the pack straight water.
Safely testing and expanding my limits.