[sph]

It's not high if you don't know how to measure your blood pressure. Your BP increases a lot if you're moving around, and not properly rested.

When you're at the GP's office, you might have been rushing to get there, you do a minute of small talk and then they strap on a cuff and tell you "oh my, it's very high", this is the reason. And it happens so often it even has a name: https://en.wikipedia.org/wiki/White_coat_hypertension

I have seen dozen of times, because of effort, anxiety, whatever, my BP being 160/110, which drops to 130/85 after 15+ minutes of complete relaxation. Many amateurs (which apparently includes most GPs) simply do not let the BP settle. The medical value of tracking BP is to know its baseline at rest, otherwise it's a meaningless number.