Allow me to set the scene. It's late at night and you're starting the last hour of a multi-hour trip home. You already knew that starting the drive so late instead of spending one more night away from home was ill-advised, but as your blinks become longer and slower you're having significant doubts about your ability to finish the trip. Just as you're debating the merits of stopping for a nap, the unthinkable happens. You nod off, cross the double-yellow line, and crash into an oncoming vehicle.
Both you and the driver of the vehicle you hit are fortunate in that an ambulance scoops you up quickly and gets you to a nearby ER where you're both stabilized for the time being. You're doing okay, but the other driver is in bad shape. He needs a kidney and some blood. Miraculously, you're a perfect match for both.
Ultimately, you make the call that you can't bring yourself to do either thing. There are many reasons that you use to justify your decision, but none of that matters--it's your call and only your call. The family of your victim goes from begging to threatening lawsuits, but there's nothing they can do. Your right to bodily autonomy is absolute. No court can compel you to use any part of your body to save the life of another person for any reason.
The family of your victim rallies almost immediately. Surely, now that you've passed, they can get your life-saving kidney. In this case, your death changes nothing--you weren't a registered organ donor and your family is inclined to honor your implied wishes. Your organs die with you. Even in death, your bodily autonomy is unassailable.
Out of the blue, your situation take a sudden turn for the worse. In the span of minutes you go from talking with your family at your bedside and impatiently asking when you can get moved out of the ER to being pronounced dead by a tired doctor at your bedside.