Some illnesses cause our blood glucose to go haywire. Colds, flu, infections, food poisoning. Sometimes the medications we take for them do the same - steroids and antibiotics, and others. Lack of sleep is definitely a factor for some of us, including me.
I had food poisoning a couple of years ago and my blood glucose was skipping around like a stone skimming a pond.
Unfortunately, there is very little we can do except be gentle with ourselves, keep on top of our chosen way of eating, and monitor them. And seek medical attention if they go too high, of course.