This ride shouldn't have been a problem but it was. As you say, low blood sugar. Only two possible causes for that: you're not recruiting your bodyfat for energy, discussed in post 47, and/or not eating anything like enough or sufficiently regularly. Also it's possible that if you're not eating enough carbohydrates in your regular day-to-day diet, you're not replenishing your glycogen, especially liver glycogen as I've discussed earlier. This latter however can be ameliorated simply by eating.

It works best for most riders, early in their training, to replace lost sugars by eating. The fat burning is a slow adaptation that takes time. It'll happen even if you eat because it's impossible or at least very very difficult to eat enough to ride without burning fat.

A full meal in the middle of a ride is the worst way to eat and the most likely to cause a blood sugar event. The stories of cyclists who ate a big meal and 200' later were either barfing or sitting in a ditch are legion.

Try this: buy a 6-pack of Ensure. Chocolate works well for most folks. Put two bottles in one of your water bottles and fill the rest with plain water. Put plain water in the other. 15' after you start riding, take a swallow from the Ensure bottle. Continue to do that every 15', by the clock. If there's any left over after the ride, drink it down immediately after the ride. Bring along a cut bagel with cream cheese. After the ride, eat 1/2 the bagel every half hour or until you sit down to a meal.

I'm recommending this particularly because I know the dosage from my wife's work on it.