People agree to things too easily in pressured settings. During the front-desk formalities at an emergency room, for example, it can almost seem foolish to insist on reading and understanding every paper before signing it.
This is a major reason why estate planners urge people to prepare advance written instructions for medical care in case of emergency or incapacity. An important function of an Advance Health Care Directive is to protect its creator from having to make important, potentially life-ending decisions in unfamiliar, authoritative settings.