Dementia and sleeping alot. What's normal?

Mom is 90 has dementia. And although not a big eater. Here lately she will go 2 or 3 days not eating. She will drink hot tea and coffee and a little water. And Luvs coke cola But she’s sleeping a lot. She’s always grumpy. But then that’s mom. But a lot worse as time goes on. I don’t know where to draw the line on normal and not normal. She was diagnosed about 5 years ago. And god luv my dad. He’s 91 and to date has been her primary. He is starting to slow down. And of course I feel as though I don’t know what to do. When to we know it’s time to get her to the er. Or when it’s the end 💕