There is a book on my bookshelf by Michael Nahm which I read with astonishment. Unfortunately this book is in German and has no English translation as of yet. It's called 'Wenn die dunkelheit eine Ende findet'. Or 'When darkness comes to an end'.
The book, well researched and based tells of terminal mental diseases and illnesses which lead to visions, unexplained bodily changes and all those things which are possibly related.
The main point here though is that of those alzheimer patients who are near death there is, in many cases, about one hour before the final breath a sudden clearing of the brain and the person becomes quite normal and can explain his or her final wishes, desires and love.
Maybe there is something similar in English - but it does seem as if there are other realities here.