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 come on quickly. The main ones are restlessness, confusion, tremors, twitches, convulsions or coma. Sugar (or better still glucose, which can be bought from your vet or a chemist) should be given by mouth, dissolved in water or as lumps. If your pet is still awake you can offer glucose with food if they will 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 or start to be sick over several days. As the disease progresses your pet may go into a coma, but will not get better if you give sugar solutions. Contact your vet immediately if your pet is unwell and they will probably want to take them into hospital.