Please make sure you have a discussion with your NOK (Next of Kin) or PoA-HC (Power of Attorney for Health Care) before just assigning that role to them. Talk about your wishes regarding blood transfusions and about organ donation. Also discuss the lengths you want the health care team to go to in the event that you will not survive the situation.
This is not a pleasant discussion. It can be very emotional, so make sure you set aside the time for it, and have the conversation with a clear mind. If they aren't aware of the JW-related issues with JW people who will most definitely assume that they have the right to be your NOK over the person of your selection and could make things difficult for your Person, they need to know this stuff - it's extremely important.
Writing a will is something that I procrastinate on, although I know it's something that needs doing.