That, my friend, is a liver dump.
One of your liver functions is to store glucose. Why? Well, I'm not sure but some one here will know. When your BG goes low your liver is prompted to release the glucose that it has stored (assuming you weren't quick enough to detect and correct the inevitable hypo) in order to bring you back up. Obviously the message here, as I think you know, is to
always carry glucose on you - Dextrose tablets are the most convenient.
Also bare in mind that once your liver has dumped it will want to regain the glucose it has lost and so your next meal might yield unusual results afterward.
Liver dumping is also the suspected cause of 'Dawn Phenomenon' (which has come back Caitycakes
) as you hypo in the night and rather than wake you up, your liver just dumps and you wake up with elevated levels.