I knew a guy from my high school who spent a really long time on Death Row in Ohio. All he did during that time was spend 23 hours in his cell and eat as much food as he could get. By the time his original execution date arrived, his lawyers made the argument that he was too obese to be executed by lethal injection. He spent several more years on Death Row while the court considered the argument. The state ultimately decided to go ahead with the execution, and he died without suffering any of the problems he thought he would have.
I would hate to be an innocent person on Death Row. I can't imagine waking up every morning and hoping to hear that your attorneys got you a new trial or a reprieve. I don't think I could handle it myself, especially if I knew I wasn't guilty.