I've been told that if your person with dementia keeps asking the same question it's because they haven't been given the answer they want. At home Ash asks me each morning whether I've slept. I then tell him in detail about my night ( I've usually been awake for a couple of hours at some point and have often gone downstairs and onto the computer). He will ask that question several times and I usually repeat the answer I first gave in the belief that if I repeat myself often enough he'll remember what I've said. It never works! After a couple of days on this holiday I decided to see what would happen if I just said 'yes'. Did that for three mornings and found that each of those mornings he only asked the once. This morning I forgot so when he asked my reply was 'no not really, my sunburn was hurting'. He then asked the question again and again until I changed the answer to 'yes'. Then he stopped asking. Not sure it was the answer he wanted just the one he could remember.
This learning curve you are on is a fascinating and if a strategy works, does it really matter how or why - everyone at home is content.
When you need to air your "no, a rubbish night" thoughts (to stay sane) then at least you know you can move on without frustration and get positive.