How low is too low when it comes to your blood sugar?

You don't have it: In addition, in my 35 years of practice, I have never seen a case of true hypoglycemia except after therapy for diabetes, or in cancer, liver or kidney disease, prior GI surgery etc. If you're overweight the symptoms are a natural response to you sugar returning to normal. A glucose tolerance test (if you've had one) is not and never will be a valid diagnostic test for hypoglycemia.