Doing some reading about blood pressure. One thing I'm learning is that BP has a pattern during the day - lowest at night, rises in morning, highest in afternoon, falls in evening. And that this pattern can cause pretty wide swings in BP. Here is a graph I found - the upper graph is systolic BP, the lower graph is HR, in each graph the upper line is hypertensives (people with high BP), the lower line is normotensives (people with normal BP).
Daily Life Blood Pressure Changes Are Steeper in Hypertensive Than in Normotensive Subjects