Dementia: I think it looks different for every sufferer.
I used to work in nursing homes. My dad also died with dementia. My mom has been diagnosed with it for about seven years, but I am sure she had it before.
She lives with us, I am her caregiver. I really think what you were in your life and your past habits exacerbate themselves when you have dementia. The past habits seem really hard-wired, even when they are now unreasonable. My mom used to eat out and shop every day. Always had plenty of money from sale of her home, and charge cards. Not so anymore, but the mindset is still there. She is pretty miserable and angry sometimes because of her limited finances (she ruined her credit, because dementia made her non-existent organizational skills even worse and she did not pay her bills correctly or at all). He money from sale of home is gone, too. She begs me to take her out to eat all the time; we try to take her out twice a week, because we know this is part of her happiness. But, in other things, she no longer has the money to order the tons of clothes and expensive jewlery, and still is upset about it and angry at us because she thinks we don't let her buy all the stuff she is used to having. There are many other similar habits that seem hard-wired and will cycle in and out of the brain, also every few weeks. On the upside, she still is quite with it as far as her ADL's. etc. and she loves kids, loves to read (even tho she can't remember what she read), loves to write imaginary letters to her friend that she never sends. Fine motor skills still good. Comprehension skills - fading. You have to explain things over and over and over and over. like its a new game each week.
I think it is very very helpful to have some expectations of person with dementia and hold them to these expectations; like cleaning up their area, folding some laundry, working puzzles. It can get simpler as disease progresses. I think it helps keep them good for longer. Like I said, my mom has had dementia for many years and I think it helps to keep them busy and have some expectations of them. Sitting and "vegging out" a lot is not good.