If you have a power of attorney for personal care, you have the option of listing specific instructions in it. These can be things like whether to donate your organs, your preference for care in a facility vs. in your home, or even end of life care. The general rule that your attorney has to follow is first to look at any written instructions, then to follow your known wishes, and last to do what they think you would want done.
You don’t have to write everything down, but you should at least be discussing your wishes with the people you have named. If they don’t know, they can’t do what you would have wanted.