What Could Cause An Elderly Patient With Dementia To Suddenly Lose Mobility And Become Wheelchair-bound After Briefly Losing Consciousness On The Toilet?

My mother 80 years old with severe dementia maybe PPA, 5 minutes after sitting on the toilet went unconscious for up to 4 minutes. At the time she was completely mobile without use of cane or walker. They cleared her medically (really?)and told us she couldn t stand or walk and they sent her to rehab. two weeks after the event they are telling us that she s in a wheel chair and can t do anything on her own. WHAT? She was completely self sufficient and 2 days later she can t stand and noone at the hospital investigated WHY. (she had a bad seizure 2 months ago after moderna vaccine) What would happen in the body for this to happen! I m trying to get a hold of her regular doctor but this is unacceptable. Thank You for your thoughts.