General anesthesia is extremely safe and is used in thousands (perhaps tens of thousands) of operations every day.
Malignant Hyperthermia (MH) is exceedingly rare -- and yes, it can be dangerous. When it occurs, it is usually triggered by agents/medications used only in general anesthesia -- not intra-venous sedation (twilight sleep) anesthesia. There are no blood tests for this condition -- it can only be diagnosed by a muscle biopsy ahead of surgery.
Best is to inquire if any members of your family have ever had MH or any problems with anesthesia -- it is usually an inherited disorder.
Ultimate safety question, assuming your family history is negative, is to have the surgery done under general anesthesia in a hospital which has Dantrolene, the only medication which successfully treats this condition. Virtually every hospital in the US is required to have Dantrolene -- in sufficient quantities -- in the hospital.
Bottom line, however, is not to worry too much about this -- it is very rare.
Dr Jacobs