My mom has declined so fast. She is in late stage dementia. She's leaning to one side and her neck down. Can things go that quickly?

Sleeping more. Unstable walking. I've noticed over last 3 months (prior to her recent decline) She wasn't getting up without help, but sitting up shuffling through her items on the table. I had her at my home from 8/22 to 9/26 when my dad fell and was in rehab. She started declining then. We found out her thyroid was low and since is back in range. She's been leaning her neck down and sleeping so much. She also takes donezepil (aricept) and my dad couldn't remember the dose before he went to hospital and rehab. The Dr. Said 30mg, but I remember my dad saying (the same Dr.) said some patients take 5-7 10 mg for late stage dementia. So if my dad was giving her more and it was decreased, would that cause her decline? I don't know what to do because it all happened too fast. I mean there were little signs she was changing, but 2 months from completely walking holding her hand, to holding her arm and body to move her and her daytime sleepines (long periods) to sleeping through the night. Whenever I check on her she's sleeping.

She also takes 10 mg of olazapine, but seriously we've cut back on that because she is not agitated as she used to be.

Can things go that quickly? Mom has had dementia since approximately 2010, so I know it's late-stage, I'm not in denial about her condition. Just want to know if there is anything I should have checked out to rule out any other possibilities.

Any help would be appreciated!

Thank you for your time and attention.

Daughter of the most beautiful mom in the world!!!