It's good that you recognized that sundowning phenomenon for what it is, friend. My mother also went through that in April when she was hospitalized. I didn't know anything about it at the time and, frankly, I was really afraid that she was going off the deep end. She also had some bad experiences with some pills that the doctor prescribed. I think they were called gabapentin. She had paranoia, suicidal thoughts, etc. Fortunately, she has gotten over all that and is not taking any hard-core drugs.
This topic is also about caregiving for pets. My elderly cat, Diva, is in her last days, I fear. She is 17 years old and last Thursday I noticed that she did not get up and amble towards her food when I put it down next to her water bowl. An hour later, she was still lying where she had been in the morning. I realized that she had lost the use of her hind legs.
Carrying her around like a baby, I fed her, washed her, and put her in her litter box. The next morning, she hadn't improved so I took her to the vet. They ran a battery of tests but couldn't really find anything wrong. They did say that her heart was beating a little fast and her temperature was a degree or two too low.
I brought the kitty home, swaddled her and laid her on a heating pad. She was so much happier! She started purring and stretched out her limbs and relaxed. Since then, I've been giving her a lot of tender loving care, knowing that I can't keep doing this for long. I notified the family that she would be making her last trip to the vet in a few days and my children have come over to say goodbye. My ex asked for her to be kept alive until he could say goodbye, but he's out of town for the week, so I don't know if I can hold off that long.