Loose rivets
You are normal. Unusual but normal. And not that rare. Put bluntly, unless you have been run over by a bus and are bleeding to death, a low blood pressure is GOOD and nothing to worry about (OK there are some very rare diseases such as Addisons but they make you very unwell and kill you very quickly - you havent got them)
the chart is c@@@. Some people have more time than sense. If the lower blood pressure - diastolic - starts with anything up to an 8 (so 74, 87 etc) that is fine. A 9 or more needs a doctor. Some big studies have shown a benefit of treating high 80s but .......
The only bit of the chart worth taking note of is
reduce salt
lose weight if overweight
moderate exercise may help
so do this and take your blood pressure at home if you have white coat syndrome. We dont mind if it goes up and down - it is the LOWEST reading when you are resting that is important
otherwise see your doctor and if he puts you on a tablet or so and controls your blood pressure your risk factors come back almost to normal.
That is about it!