hi i had gone through your query and understand your concerns. i would come up with two possibilities to fit your mother condition .these include
1.the first one may be,ORTHOSTATIC HYPO TENSION;change in position from sitting or lying to rising position may cause in sudden drop of the blood pressure .
2.second possibility is,CERVICAL SPONDYLOSIS;is due to degenerative changes in the cervical spine
-general poor health
-obesity are the predisposing factors.
i advise you taking Homeopathic
medicines gives safe and permanent cure for your mother complaints
consult your local homeopathic physician for correct diagnosis of the case and remedy to fit her complaints
I hope this is helpful for you, thank you