The Terri Schiavo case illustrated the importance of having a Living Will.
More importantly, it also, unfortunately, illustrated the pitfalls of not having a Living Will.
A Living Will (or, in Pennsylvania, an Advance Directive for Health Care) allows you to choose someone to make health care decisions if you are unable to do so. It also allows you to direct whether life-sustaining procedures should be used if you have a terminal condition or are permanently unconscious.
It must be signed before two witnesses, and no notary is required.
A Living Will, therefore, is an excellent, if not imperative, tool to have in order to ensure that your own desires are followed in the case of such an unfortunate event.