I decided to do some long-distance (all-day/multi-day) cycling in Europe as a complete amateur, and quickly became aware of the feeling of running out of glycog

I decided to do some long-distance (all-day/multi-day) cycling in Europe as a complete amateur, and quickly became aware of the feeling of running out of glycogen, so I just loaded up on simple carbs like breads and sweets, and could instantly feel myself re-energized as I ate them through the day. Then, I think it was a few days in I'd been just downing pure carbs, was in the middle of nowhere on the bike and started rapidly feeling deeply unwell: zero energy, brain fog, heart racing, felt like I was about to vomit and then die. Pulled off to the side of the road and somehow the thought came to me "... electrolytes?" Luckily I had a small packet of electrolyte powder which I mixed with a tiny bit of water and downed. Recovered almost immediately. Just an FYI - relying on carbs alone only lasts for so long.