Hello, thanks for the query to H.C.M.
Please don't mind that I am very straight forward and I will tell you those things witch are good for patient but not for attendants.
In your query , answer is hidden of your's mother illness.
She didn't have any physical problems as you mentioned above because all tests are normal
Answer is here she has 4 KIDS and 6 sisters and "SHE LIVES ALONE".
Twilight age and sedentary life , so anxiety
It might happens that she will not say any words from her mouth but try to understand what she want.
She will be alright within short period with love & affection.
Regards and good luck to grand ma. Dr. HET