... Hepatic glycogen is high, as HTG suggested. Do you eat much fructose?... Any difference in a morning vs. a PM shot in terms of onsets of the shakes?...
... You are somewhat insulin insensitive. What's your diet like?... Lots of carbs all day long?
... Could be any of a number of things related to epinephrine, somatostatin or glucagon release.
.... Have you used a ketogenic diet before?... SOme find that adapatation to ketosis is very long lasting: even after months on a higher carb (e.g., Zone) diet they can still show ketones. IN this case, your brain may be able to fuction well w/o glucose and your liver is good at making ketones.
FYI, you are not the only person who can do this. I know someone who could do 15IU BEFORE a workout lasting an hr or so and then has waited another couple hours after the workout w/o food, dealing with the shakes, delirium, cold sweats, etc., only to make it out of this as slin levels decrease and the hypoglycemia is gone. No carbs or protein for 3hr after 15IU AND a workout. He would do this to see how high his appetite would go so he could eat amazing amounts of food and once just decided to see how long he could last. NOT THAT I'M SUGGESTING THAT YOU OR ANYONE DO THIS!!! (BTW, this guy is a crazy mofo.)