--and would highly recommend a much longer glucose tolerance test, with both glucose and insulin levels determined with each draw, to see the patterns.

Specifically, as Mrs. D says, you would want to know your fasting insulin level, to see if it is relatively high (that may be what is keeping your fasting glucose in a normal range, and it may signal insulin resistance, in which the body has to produce more insulin to keep blood sugar in check). Then, you would want half hour draws until at least 4 hours to watch the pattern of insulin and glucose rises/falls. What often happens in the insulin resistant is that their blood glucose does not rise that much in the first hour and a half or so as the body reacts to the glucose challenge by producing a big spike of insulin--this spike, however, tends to drive glucose levels down below one's fasting level in hours two/three (which may be happening here) until first insulin and then glucose "normalize" in hours three and four.

This pattern of "reactive hypoglycemia" is quite common among the insulin resistant.