My mother is 90 years old, and in a split second she stopped walking. Is this common in the elderly?

I agree with Spoony. It just takes time. My mom didn't want to stand up either for awhile, but they get over it once you get into a routine and they know they can be helped and safe again , and then it's smooth sailing...

90-year old, bless her heart. I would say at this age is more common than not. I am not saying this happens to all of the 90-year olds, but I wouldn't be surprised.

While she's being transferred, you just hold her hand and keep reassuring that she's safe and that you won't let her fall.

I would assume that the part of her brain that knows how to walk has been affected. At her stage of dementia, I would believe that she is not refusing to walk on purpose. She might have had a near fall that scared her, but I bet she doesn't get over this, because her brain is too damaged.

I'm definitely no expert, but I do believe that elderly person can just "give up". However, I don't know that this is totally the case for your mother. Dementia is defined as the loss of mental functions such as thinking, memory, and reasoning that is severe enough to interfere with a person's daily functioning. Sometimes, these parts of the brain that are involved with learning, memory, and decision-making are affected by dementia at different times. Your mother may be affected one day with some symptoms and another day with an entirely different set of symptoms. Some of these symptoms can change and others will remain. Most of the time, the symptoms appear to worsen over time. Sometimes these symptoms can cause changes in their personality, mood, and behavior. Her decision-making skills may abruptly become "damaged" (for lack of a better word) and she is not be able to "reason" that she "isn't" going to fall performing a simple task. It's so hard to know "why" it happens so quickly, especially when your loved one might have been doing well for awhile. As long as the lab work and other diagnostic tests are negative, there is not a lot that can be done other than the repeated reassurance that you (or another caregiver) are there and won't let anything happen to her. The important thing is to keep a vigilant eye, because strokes can happen quite easily in the elderly. An abrupt change in your loved one, whether it is emotional or physical in nature, can be an early warning sign of a stroke. In that case, seeking immediate medical care is the BEST ADVICE! I wish you well.