A living will is a legal document and is sometimes known as an "advanced health care directive". It provides instructions as to your medical wishes should you ever become incapacitated and are unable to speak your wishes.  You need to have this in place BEFORE the tube goes in, before you get shot, before alzheimers kicks in, etc.  For more info on this topic, check out the upcoming article on "How to Create a Living Will - and Why" in the Health section of the Survival Guide.