How long do the fatigue and 'brain fog' last after surgery with general anesthesia?

It depends -- on your age, the specific drugs used, how long the surgery took and how healthy you were to start with. These days, most general anesthesia drugs are fairly short-acting, which means you wake up quickly and the drugs are mostly out of your system within a few hours, said Dr. Carl Rosow, an anesthesiologist at Massachusetts General Hospital.

But tiny amounts can linger for up to seven days -- enough so that you may not feel completely normal, especially if you also have a drink or two.

Moreover, if you are one of the unlucky 20 percent to 40 percent of patients who have nausea and vomiting after general anesthesia, that can add considerably to your recovery time because of dehydration and weakness from not eating, said Dr. John Ulatowski, director and chair of the department of anesthesia and critical care at Johns Hopkins Medical Institutions.

It's actually quite difficult to sort out how much of the fatigue and ''cognitive dysfunction," or temporarily decreased intellectual function, that often follow surgery is due to general anesthesia and how much to the surgery itself. Some cognitive dysfunction can occur even after regional anesthesia, in which pain is blocked in one part of the body and the patient is sedated but not rendered fully unconscious. That suggests, Rosow said, that part of postsurgical malaise may be due to the physical stress of surgery, including the outpouring of stress hormones and inflammatory substances called cytokines.

People also vary widely in their response to general anesthesia drugs. For an older person having lengthy, major surgery, it may take six months to feel normal, though much of that probably would be because of healing from the surgery itself. A younger person having a short, minor operation may feel fine and be back at work the next day.

JUDY FOREMAN