"Hyperglycemia (high blood sugar) will NOT kill immediately, and short-term hyperglycemia is unlikely to have any adverse affects.
Hypoglycemia (low blood sugar - caused by TOO MUCH insulin, or too much exercise or not enough food, combined with insulin) CAN KILL, often rapidly."
I'm not trying to scare you, but it's very important to know, NOT to reach for the insulin when a diabetic animal starts acting strangely.
Please read up on the basics, so you can recognize the signs of a hypo, and keep something sugary in the cupboard - glucose syrup or honey or maple syrup etc.
Best of luck!
ETA
http://www.petdiabetes.org/hypoglycemia.htm
