Granted. You never age. You watch all your friends and family get injured, become sick, die. You tire of losing people eventually and become a hermit. Your physical health is no substitute for human companionship, though, and you start to lose your grip on reality. You never grasp it again. All the money you've built up through simple compound interest ensures that you do receive care, but your doctors notice that no matter how hard you slam your head into the wall, how many drugs you are given, how little you move for weeks on end, you remain in peak physical condition. They begin to study your physiology. Passive at first, they start to take it further and further. They never discover the font of your health, but they never stop trying, never stop the cutting, slicing off bits of you to put on the microscope slides, never stop the needles to suck out your fluids and put them into the centrifuge. That your mind had gone before they started the years and years of study is a mercy to them; they don't see you as human. They couldn't do what they do to you to a human, after all.