As Ken has stated, make sure you contact the hospital clinic for clarification on what you should and shouldn't do regarding insulin etc. I wouldn't worry to much about being anaesthetised, these people perform operations all the time on people with diabetes, and your blood glucose is closely monitored throughout the operation.
In 2004, I had a 4 1/2 hour operation and always felt assured that I was in safe hands, all the medical staff will be fully aware of your diabetes, so take on board what advice they give, and do write it down should they not give you a written explanation of the pre/post op procedures. As you will appreciate, I don't want to comment on what you should do prior to the operation, as the advice and procedures may have changed somewhat since 2004.
Best wishes and hope all goes well!
Nigel