Have you noticed a very strong tightness in your neck and shoulder muscles during these flare-ups. I have been fighting high BP for many years and have many flare-ups, especially when I'm on my computer for several hours. My neck and shoulder muscles get so tight that I cannot turn my head, When this happens my BP explodes as yours does. So high that I've had to be hospitalized. I've been told that when this happens my heart cannnot pump enough blood to my brain so my BP flies off the charts very fast.
I wish you the best of luck in finding the answer....Bill