Carbonel, my 6 year old DD has low blood sugar moments. There is no point in going into the details of the 'meltdowns' except to say they are ugly. When her body is all 'balanced' - ie, she's been feed, she's hydrated, she's slept well - then she's a perfectly behaved child. But if the balance goes off, and her sugar dips, she turns into a monster until I can fetch her a snack and a drink.
I took her to the doctors who were dismissive. They said low blood sugar is within the realms of normal. When we've managed to take her sugar levels on one of these episodes its been between below 4.
I have to say, though, that I would not be surprised at all if something physical was ever found wrong with her. She suffers serious insomnia and also complains daily her body aches.
Diabetes runs in DH's family and I read somewhere that suffering low blood sugar can be an indication that a person is more likely to develop diabetes type II when older. I don't know how true that is, but out of curiousity ask if diabetes is in your family?
As far as managing it goes, we do probably the same as you and make sure meal times and snack times are as regular as possible. She doesn't have the best diet in the world, though. Refuses vegetables and absolutely craves sugary things which could be part of the problem.
I would say that she has probably had this since she was about 3.5 years and it was at its worst at about 5 years. She is now 6.5 years and it is a lot better. The low sugar meltdowns are less frequent.
I don't normally hear of other people with similar problems so its actually a comfort to read your post, although I'm sorry I've not really given you any advice.