My MIL who has advanced Alzheimer's is the same, although she isn't here in the UK, she is in SA bring cared for by one of her daughters plus round-the-clock nursing support.
One week she is practically comatose, laboured breathing, refusing food and we start looking at flights and dates.
Then we get a phone call that she is awake, bright as a button, in her wheelchair and eating chocolate. The doctors tell her daughter they've not seen anything like it. She was diagnosed at age 66, and is now 86, severely affected for at least the past 8 (no speech, having to be fed, incontinent, no mobility).
We are removed from the situation, just grateful that she has superlative care. It must be so difficult for you, Kitty, you have my sympathy.
We've just had another elderly family member diagnosed ...