Many people have strong views on the type of care they want or don't want to receive if get very sick. You can preserve your decisions with a living will which informs medical professionals of your wishes in the event that you cannot express them yourself.
Unfortunately, without this legal document, disputes over your care can arise. Even if you think you have clearly communicated this information in other ways, there could still be room for interpretation if you don't have a living will or health care proxy. This was the situation facing medical professionals and ethics consultants in Florida recently.