Brother got his taken out at age 21. Surgery wasn't bad, nor was the first few days. When he started cutting back the amount of hydrocodone he was taking, that's when it got pretty rough. Somewhere around a week after the surgery, as he was just starting to get back to normal, a scab in his throat broke off, ripping open some sort of blood vessel. It dripped continuously down his throat for a couple days before it really got to bleeding. First indication of that was his coughing and turning the bathroom into what looked like a crime scene.
He'd bled quite a bit down the back of his stomach by the time they finally got the bleeder in his throat cauterized again, and then they sucked at least a liter of blood out of his stomach. He was pretty much fine after a night in the hospital, but had to go through the whole no-food-except-liquids, extreme-sore-throat thing again, essentially starting over at 0 with no painkillers.
Supposedly difficulties like that happen in only 1% of cases though.