@Mweirum
I hope you see this at some point. Sorry for the very late response. I haven't visited here for a long while.
At the time my previous posts on this thread were written, I was diagnosed with Postural Orthostatic Tachycardia Syndrome ( POTS ) and with "hypoglycemia" based on the GTT results. My doc did not make any connection whatsoever between the two.
Since then, it has become apparent there is a connection. POTS is a form of autonomic dysfunction. It is very likely that part of the dysfunction involves "rapid gastric emptying" or "gastric dumping," where the contents of the stomach are dumped too quickly into the small intestine leading to spikes in blood sugar when high carb meals are eaten.
Here is a nice lecture from a PotsUK conference which lays out the connection.
Although I went hypo with the GTT, I never caught a significant hypo with home testing after eating regular meals. I tend to spike a lot with moderate carb meals though. I think many of my symptoms were more the result of rapid spikes and fluctuations of blood sugar, rather than simply being too low.
Anyway, the actual cause doesn't seem to matter. The solution is the same: LCHF diet. I still have POTS, but keeping my blood sugar under control keeps my symptoms way down.
Hope this helps.