I've addresses this issue before (here and here), but it certainly deserves repeating. Forbes recently published a terrific article emphasizing the importance of completing a living will (aka advance health care directive) and what happened to one family without one. To summarize, the deceased suffered a brain aneurysm and soon fell into an irreversible coma. He was essentially brain dead, save minimal brain activity. The family, still suffering from the shock of this event, was then confronted by the hospital who desired to take him off life support and let him die. The family was unsure what he would have wanted and fought to keep him around at least a few days longer to allow them and other out of state family to say their goodbyes. The hospital disagreed and a standoff ensued.
Not much later the minimal brain activity he had left eventually ceased. However, without advance direction from their deceased father, the family was left with significantly greater expense and stress than necessary.
As part of any estate plan I draft, I include a living will. This gives my clients the opportunity to think through and decide what is to be done if they are to fall into an incurable and irreversible condition that, without life sustaining treatment, will shortly result in their death. It is not an enjoyable conversation, but an important decision that will relieve their families from many of the difficulties suffered by the family discussed in the article.
If all you need is the living will by itself, the Nevada Department of Health and Human Services has provided a form along with pages of useful information here.