In my opinion this is a great subject, be it someone is young, old, healthy or ill. In the last few years I have seen in my family things go a little side ways because a couple people did not have their wishes in order. Sad but true. Here in Georgia USA, we have something called an "Advance Directive for Medical Care". This gives options from of the care you wish for and that of what famiy member or friend you wish to follow through with these wishes, at the end if no one is available that is listed then it would be up to the doctor at the time, but the form still states exactly what I want and when, Recently to do multiple medical conditions, I have signed a DNR "Do Not resuscitate". Other areas might call them "Living Trust" or "living Wilks". What we did was contacted an attorney for they usually will give some misc .free advice and knowledge what what your options could be for your area. At times there is Department of Aging or a local senior center might be able to assist you and what information you are seeking. Either way, here we have to make sure that many have copies, fire department, each of the ambulance services, hospital, hospital groups, primary doctor etc... always have a copy at home and ready for when you might need it. There is always checking out Hospice assistance when time gets closer also. Could possible also give a trusted family member or friend a "Medical Power of an Attorney" with your instructions of course, thus would only come in to play if you are incapable to make your own choices at the time.
Hope some of this is helpful to you, again I believe everyone should consider doing something like this, just settles the mind in my eyes.