Well, you hope you don't feel anything... Are they using propofol alone? Has more research been done on how good of a painkiller it is vs a memory eraser?
You just pass out on the table and wake up in a bed something like 40 minutes later. I could remember everything up to feeling the effects of the anesthetic and beginning to pass out, but nothing thereafter.
I also received lidocaine, and felt rather great afterwards for the next few hours.