You say your bs was "awesomely low" in the morning...then you tell us what you had for dinner. What about between those times? Did you have carbs with other meals? Did you check your bs between then & dinner?
If you didn't have carbs, possibly you went too low & your liver did a glucose dump. If you did have carbs, what makes you think the sandwich was the culprit? More info helps us give better opinions.
