When a cat's blood glucose goes low, their body will react instinctively by releasing "glucagon", "glycogen" and counter-regulatory hormones into the blood stream. This causes the BG to rise, usually significantly. It usually makes them stay higher for a day or longer too.
By "low", that doesn't have to mean hypoglycemic low. Just lower than what the body is used to. A cat who has been running in high numbers in the 350-400 range can bounce if the numbers drop a couple of hundred points. Because the cat isn't used to BGs in the 100-200's range.