There are two important complications to be aware of:
Low blood sugar (hypoglycaemia) – If this is untreated it may result in permanent brain damage. Symptoms develop rapidly with restlessness, confusion, tremors, twitches, convulsions or coma being the main signs. Sugar should be given by mouth, dissolved in water or as lumps. If your pet is still awake it may be offered food and should eat voluntarily. Contact your vet immediately if these signs develop.
High blood sugar (hyperglycaemia) – This usually develops more gradually and your pet may become unwell over a number of days. As the disease progresses your pet may go into a coma, although will not respond to sugar solutions. Contact your vet immediately if your pet is unwell and they will probably want to take him into the hospital.