By far the worst 'dementia-Christmas' event for me, was a couple of years before my mother was bad enough to need a care home.
Sister and niece, visiting from the US, were staying with her for a couple of days before Christmas Eve, when I was driving the 60 miles to pick them all up to come here.
On Chr. Eve afternoon, sister phoned to say my mother was sorry, but she really couldn't cope with all the fuss any more, would rather stay quietly at home.
A shame, but OK if that was what she wanted. So I took down her presents and plenty of nice food, brought sister and niece back here.
Roll on a couple of hours, everybody else was out (Harry Potter film!) and my mother was on the phone, absolutely furious.
What was she doing all on her own on Christmas Eve? I was a terrible daughter, she was cutting me out of her will, etc.
I don't know when I've ever been so upset. Of course it was useless to explain that of course she'd been invited - she hadn't wanted to come. She simply couldn't remember. I offered to go down at once and pick her up if she'd changed her mind - no, she didn't want that either - still furiously angry with me.
I was in tears for ages.
Typically for dementia, by the time I phoned on Christmas Day, thank goodness she'd forgotten all about it.