Swing of BP from high to low,one of important illness we should thinking about is Pheochromocytoma;this is a tumor of chromaffin cell that secrete catecholamines,causing hypertension;this may be paroxysmal(45 %),that mean the secretion is irregularly,when a lot of catecholamines go to blood steam the BP will be very high when the secretion stop the BP will down to the level of before.As a 78 years old lady her BP could be in low side.Tell her doctor looking for this illness and do some blood and urine test to confirm the diagnosis.You mention about stroke,there are clinical data showed that if BP swing from high to low in first 24 hours of the stroke that means poor prognosis;die in 3 months.

Some medicine will cause this.But your doctor should know if it is any thing he prescribed.Do you take anything he doesn’t know about?

1) medications. (take BP med and have low BP, then it rebounds to high BP when it wears off) – clonidine is famous for this
2) Over the counter herbs/remedies (ephedra, caffeine)
3) Illicit drugs – 78 year olds in Philly actually do cocaine!
4) Autonomic instability – sensors in the neck measure our blood pressure and adjust our heart rates. As we become older this system may fail. Often presents as fainting spells.
5) Adrenal tumor (1 in a million) – ask primary doc to screen urine.

That’s off the top of my head.

Since there is no indication of bleeding, the only other thing that I can think of is an allergic reaction to her medication.