If you can not contact your vet, call any vet - and get additional instructions. Your pet will probably have to go to the vet immediately. Whenever a pet has a hypoglycemic attack, you should contact your veterinarian. Future doses of insulin should be reduced until a proper insulin dose adjustment can be made. Making the proper adjustment will probably be based on the results of a blood glucose curve.
Exercise can cause hypoglycemia.
If it is out of the ordinary, even a small amount of exercise can cause hypoglycemia. Read some personal experiences from owners who have learned this the scary way. Nigel Goes Hypo. A well-written account of a hypoglycemia episode, and the suspected cause. But Bobbi was kind enough to write a song that helps relieve the stress of being an owner of a diabetic pet.