Okay, it's definitely not appendicitis and it's most likely not Flesh-Eating Parasitic Hellbeast Disease either. Probably a kidney infection? Which is bad, but not surgery bad or "set your affairs in order" bad. I'm still waiting on lab results for a definitive diagnosis but the doctor assures me that I am not dying.
EDIT: "Abdominal pain, cause unknown, call us if anything changes." Fuck! It's equal parts aggravating (thanks for the help, guys) and embarrassing (they presumably think I'm a crazy drug-seeking hypochondriac now).