There can be several reasons of her symptoms although without being able to examine you I can not offer you the specific advice on diagnosis and treatment that you need, but I would try to provide you some relevant information about your health concern. It may be vagus nerve issue as this nerve supplies in many major organs like heart, lungs, stomach, palate, esophagus etc. Therefore, vague nerve damage or compression can cause bradycardia (decreases heart rate), arrhythmia, voice changes, difficulty in swallowing, gag reflex, constipation and incontinence but its damage does not cause dehydration. Therefore, I would recommend you to consult her treating neurologist who can evaluate the details of her case and could better determine the insight of her situation. Hope this helps.
First, address the complete and utter negligence of the hospital staff KNOWING she had an adverse(ALLERGIC) reaction to the barium the first time they NEVER should have given her that test again. This could now be a permenant condition.
The Dr. above is only saving face which is what doctors do. Common sense SHOULD TELL HIM this is outrageous. Never go back to that hospital or those doctors again because they could make the same mistake AGAIN but next time they may not be able to revive your Mom. Find a homeopathic Dr. that can help with the neuropathy and nerve damage. Believe it or not, Yoga is enormously helpful. Deep breathing actively lowers body acidity, raises alkaline levels, and helps the ENTIRE BODY HEAL. Sometimes it's the only thing that can calm the Vagus Nerve...ample doses of clean oxygen. When the oxygen levels go down, acidity goes up, then we are open to a host of cell damage and infection. Stomach issues often CAUSE vagus nerve damage--like acid reflux.
It certainly sounds like Vagus Nerve Damage, and this can be irreversible. Doctors are poorly trained--for example: a Neurologist will have little to NO training or accessable education in Endocrinology, they'll keep the fields seperate which is where our health goes remarkably downhill. This in turn "keeps" an enormous amount of vital information from them. Like how they are curing life-threatening Epilepsy & even Autism with Trans Cranial Magnetic stimulation of the Vagus Nerve. Look up John Elder Robison--he's a huge advocate and a friend. He'll tell you all about it!
FIND your mothers cures--DON'T wait for doctors.