All surg is serious
There's always general risks in all surgery involving general anesthesia
but all care is taken monitor u during the procedure.
The surgery u described is called antral windows that open the openings of the sinuses wider 2 allow them 2 drain much easier. It is a proven procedure over the years & i would not worry about it. Any fears talk 2 ur ENT surgeon. Bring a list of ? 4 him/her so u don't forg.