--testing for celiac/gluten sensitivity would also seem to be in order--at least the serological tests (anti-gliadin IgG and IgA, anti-transglutaminase igA, and total IgA; this last, if not in the normal ranges, can skew the results of the other mentioned IgA tests).

Moreover, that zoom/crash in the 5-hour glucose tolerance test--the reactive hypoglycemia--implies insulin resistance/metabolic syndrome/pre-diabetes (though there are certainly people who experience a hereditary form of this--but wild swings in blood sugar either way are not good for nerves). Were insulin levels checked along with blood sugar levels during the test? That can often be revealing.