Show that "according to the leading theory ... surgery and anesthesia trigger the release of stress hormones, such as norepinephrine, that in turn activate inflammatory responses in the body and undermine the workings of the immune system." (from here).
Also, there is strong evidence that Anesthesia can trigger depression and cause other cognitive problems that can take a long time to resolve. (look here.)
I have noticed that since my appendectomy, I've been unusually blue. I've also had all the things that can be inflamed become inflamed -- headaches, joint pain where I've had arthritis, muscle soreness and now my Bell's palsy is flaring up. I had no idea that Anesthesia could do this -- I knew the bits about not lifting more than 6 pounds and that Anesthesia could take days to clear out of your system, but I had no idea there were so many long-term effects. I'm going to work with my Doctor to get this inflammation down and determine if my feeling "blue" is something we need to treat as well.
So, if you go in for surgery, be aware of this -- I certainly wasn't and this has been a rude awakening.