I have low BP and have had it for years. What concerns my doctor more is my low heart rate, which 40-45 is about normal for me. I actually failed an FAA mandatory yearly physical and had my license suspended for almost 3 weeks.
I had to go to a cardiologist and had a bunch of tests done and they came to the conclusion that I over-exercised. So, I cut back on my running, swimming and biking. My wife still swims and bikes, but she has no issues.
My BP is now like 150/65, which the cardiologist says is good. The 120/80 is a guide, but not a must have to be healthy. My heart rate is around 45-50.