Does dementia speed up in the later stages?

Or does it just seem to? My 85 year old mother has lived with us for 5 years and it seems that she went from stage 4-6 within the past year and she consistently displays all markers of stage 6. She does not have any infections or illnesses. She walks with a walker but is easily able to get up and down from her chair or bed.

It just seems her memory is drastically worse. Also, every so often she has swallowing problems but I thought this was a much, much later occurrence?