My mother (93) with dementia got worse after a bout with the flu. Is this common?

Yes. Give her extra fluids, allow her to rest and give her extra TLC!

Thank You

My mom has dementia. Every time she gets sick, I see a change in her and it usually takes more and more out of her mentally and physically. I think this is probably normal, due to the changes in the brain. Ask her physician to be certain. Hugs and prayers

Yes, very common for someone her age to need a long recovery period.