Hypoglycemia, low blood sugar, runs in my family. It is not the kind associated with diabetes, but is called Reactive Hypoglycemia. It could be considered a food allergy. Certain foods cause the blood sugar to plummet suddenly, leaving you feeling shaky and trembly inside. Eating sugary foods makes it worse (this is why it is not associated with diabetes). My mother and an aunt have it and I have it to a degree. We've learned to eat a combination of carb. and protein (like cheese and crackers) when a spell is occuring. My mother has fainted several times because it got too low, too fast and wasn't able to get to her cheese and crackers. However her blood sugar is always normal, but probably because it is checked when she isn't having a spell.
If she gets too hungry (like fasting for a drs checkup) she has problems, but also certain foods seem to trigger it--often fruits.
Since being Celiac 2 years ago, and now gluten free, I haven't had problems. I wonder if it was related?