Canine hypoglycemia is caused by abnormally low glucose levels in the body, much like humans. When canines go into hypoglycemia they can suffer from weakness or seizures.
Common in small dogs, rare in larger/older dogs. Symptoms include disorientation, weakness, anxiety, and seizures in serious cases. Prevention -- small meals throughout the day rather than one large meal.
Hypoglycemia, in dogs as well as humans, is a defect where the body doesn't release enough blood sugars. It can be treated by giving the animal sugar if he or she is listless. Consult your vet.