Simple. First, check and see how high your blood sugar is, say, 30 minutes after a meal, so you have an idea of how it is, soon after eating. (Of course, I mean, when you are post-op) Then measure your blood sugar when you have the symptom. If the blood sugar is low, it's hypoglycemia. Even if it isn't low enough to diagnose hypoglycemia, if it is lower than usual, it's probably reactive hypoglycemia. Whether you had sugar/sugar alcohol or anything that includes more carbs than you usually take, will also be a hint.
What Roo has pointed out as you have now, is more likely to be hypoglycemia, because you are taking diabetes meds, and your digestive plumbing is still normal.
Though, sometimes, the difference is not all that clear, actually.

That's another reason why the two are often lumped together. I was just being techincal with that post.