You have the right to give instructions about your own health care. You also have the right to name someone else to make health care decisions for you.  However, you must PLAN or the court may plan for you.

Your "advance health care directive" (AHCD) or "advance directive" includes both an "individual health care instruction" and a power of attorney for health care (PAHC).  A PAHC is a written document designating an agent for health care decision-making.  PAHC has also known as a "durable power of attorney for health care.  You should also have a durable power of attorney for financial matters. (DPOA)  

The AHCD, PAHC and the DPOA are complimentary documents and must be drafted as companion Estate Planning documents to avoid ambiguity or conflicts.  In addition to your health care instructions your AHCD can also nominate specific persons to become the conservator of your person and/ or estate if legal court proceeding are ever brought to have you

Unless otherwise specified in the document, the authority of an agent becomes effective only on a determination that you lack capacity, and ceases to be effective on a determination that you have regained capacity.

This is Life Planning.  "Capacity" means your ability to understand the nature and consequences of a decision and to make and communicate a decision, and includes in the case of proposed health care, the ability to understand its significant benefits, risks, and alternatives.  A serious accident can cause you to loose capacity for a period of time.  Your Plan springs into action when you need it.