I don't want to spoil the story for those who haven't yet read it, but it illustrates one of the dangers in oversimplistic attitudes to informed consent and truth telling. You might have the wrong patient. People have lasted less time or considerably more than their physician predicted.
Medical error happens.
Indeed if there is any truth at all in doctrines of the effects of state of mind on health - psychosomatics, the placebo effect, the role of stress, etc. I have noticed among my students and colleagues that doctors may tend to despise Dr. Siegel's book, while experienced nurses love it and say it is obviously right. True patient autonomy ought to start long before somebody gets sick and comes to the hospital. And when someone does get sick I fully support that person's right to choose to go to a doctor or to treat oneself or try natural methods of healing or prayer or whatever one may choose. But once one enters a hospital the situation changes.