I have had the same symptoms you describe, much like an extreme version of hypoglycemia. I have read of others with Lyme who describe their blood sugar suddenly plummeting.
I learned that it was important to eat every couple hours, even when I didn't feel hungry. There were times I had no appetite and I simply didn't feel hungry. Only when I felt suddenly faint and shakey and even nauseous did I realize I hadn't eaten in 5 or 6 hours. It doesn't mean you should overeat, so adjust meals to be smaller accordingly. On the flip side, many Lyme patients get too thin, so also make sure your calorie intake is sufficient.
An apple or carrots are definitely better than a candy bar as the fiber in the apple slows down the natural sugar absorption. A little sandwich is better than a pure carb snack. The problem with the quick fix of some sugar is that while it does help boost the blood sugar quickly, if you don't eat anything else, you'll just promptly crash again. I find when I eat sugar, I just end up feeling worse. That's really hard for a sugar lover like me.
So keep a good supply of healthy snacks at home and at work, and set a schedule to eat every couple hours. Prevention is the best approach to this symptom.
PubMed brings up no reference to "retroreactive hypogylcemia"
Google doesn't either.
I think that the person who told you that mis-spoke.
Sugar: It's probably always best to limit your white sugar in-take since it's empty calories and doesn't offer other nutrients like, say, an apple does.
Sugar is sugar. Whether it comes from a piece of bread or a candy bar it has to break down into glucose before it can pass through the intestinal wall to be used for energy.