Are you talking about a rebound? A rebound happens if your sugar levels go dangerously low. Your body reacts by releasing glucose from your liver. You usually wake up high, because your liver over-compensate and the resulting high BGs are usually hard to get to go down.
I've done that one before1! I believe some call it the Dawn effect - I always called it the Bounce back effect :-) I don't know if there is an official name for it..