I have a sister age 89 who is having blood pressure readings to vacillate from high systolic and high diastolic but then within 2 hours it can reverse and the systolic will be lower and the diastolic can also be lower and this goes on throughout the day. She is on Diovan 160 mg and has been told to double the dose and eventually it will come down and somewhat normalize but then it repeats the same ups and downs of these values. She is relatively sedentary and the higher systolics can be after sleeping all night in the early morning hours. She has had episodes with A-fib and fast heart rates. Is she in danger of having a heart attack or a stroke with these vacillating readings?