anesthesia
"Was given propofol for a colonoscopy a few years ago without incident--it was quick acting and then vanished immediately afterward with zero negative effects.  Conversely, a week ago had surgery that required anesthesia and was given fentanyl--amongst other odd side-effects this medication made me feel loopy and goofy for a full five days afterward...so unsettling.  I hope never to experience the fentanyl version of anesthesia ever again."