It turns out that my mother had a small stroke. The doctor says that she probably had it a few days before she fell, and didn't realize it. She's suffering some memory loss, but the doctor says that's probably temporary. They are keeping her in the ICU for a few more days, and will give her an MRI. She will need physical therapy and occupational therapy during her recovery.
My mother was a physical therapist for almost 50 years. I hope she remembers that when she's a PT patient for the first time in her life.