If I'm not mistaken, the top number in your BP (the 120 in 12/80) goes up and down quite easily based on whats going on around you and the docs are as concerned with it. Its the lower number which they are more concerned with.
According to the American Heart Association: Typically more attention is given to the top number (the systolic blood pressure) as a major risk factor for cardiovascular disease for people over 50 years old. In most people, systolic blood pressure rises steadily with age due to increasing stiffness of large arteries, long-term build-up of plaque, and increased incidence of cardiac and vascular disease.
They also stress: Your healthcare providers will want to get an accurate picture of your blood pressure and chart what happens over time. I've learned that when a doctor says "over time" he means years not hours, days or weeks
So don't worry about random, high readings here and there especially with the top number.