Youre right that blood pressure varies. If you dash up two flights of stairs or pick up something heavy, it may surge 30 to 40 points or more. The strain doesnt have to be purely physical. Arriving late for your doctors appointment or being worried about work might also cause a temporary spike.
But blood pressure is important as a reflection of the average stress on your arteries. So its the average reading thats important, not the ups and downs.
It sounds like you measure your own blood pressure at home. Thats great. I suggest taking a few measurements during a routine day and then averaging them. As long as you feel fine, dont get alarmed or misled by an occasional high or low reading.
For many decades, doctors have used readings above 140/90 to define high blood pressure. But recently, we realize that certain people should strive for lower numbers and other people are better off with higher readings.
For example, people with diabetes or kidney disease should aim for a lower average reading, around 130/80. And people over age 80 might do better with a blood pressure of 160/90.