You may be confusing living will with a last will and testament.
It may be helpful to think of a living will as "health care directives". So that now, while you don't have dementia, you can spell out your wishes and who has the authority to act on said wishes, when you can no longer make decisions.
It may be helpful to think of a living will as "health care directives". So that now, while you don't have dementia, you can spell out your wishes and who has the authority to act on said wishes, when you can no longer make decisions.