I have a cousin who, along with her husband, has been diagnosed with dementia. Over a period of a couple of years, they began to decline to the point where they could no longer take care of themselves. The bad part is they thought everything was fine, even though all those around them could see that they were going downhill, and this couple refused to seek any help. Eventually, they got so bad that their physical health began to be impacted, and they Finally agreed to see a doctor. As part of their diagnosis, they were given a 30 question "test", and they both failed miserably....she got 7 right, and he got 12. Fortunately, they are in good financial shape, and have been placed in a very nice care facility where they can be taken care of properly....for years, if necessary.
Dementia would seem, to me, to be as bad, or worse than being totally disabled physically.