Two important documents that everybody 18 and over need to have is a Living Will and a Healthcare Power of Attorney. These are essential to conveying your wishes regarding your health care and designating a family member or other person of your choice to make health decisions if you become incapacitated.
These documents are readily available from many health care organizations. A good resource can be found here (Franklin County Recorder)
DO NOT wait until you are already in the hospital and very ill. If the notary cannot determine that you are aware of and understand what you are signing, the notarization cannot be completed. Get these documents BEFORE you need them and have copies available to provide your doctor and for your designated representative.
This will give you and your family the peace of mind, knowing that your wishes will be followed.