I've noticed that over the months the trend has been downward and today, measured during moderate activity (housework) I recorded a score of 102/63 at a pulse of 55 bpm

This seems a bit lowish but I'm feeling great

Weight is 60.5Kg and this gives me a BMI of 18.6 which is borderline... NHS Choices says it's OK though...
Question is, is this blood pressure reading OK and just a result of my fitness and healthy lifestyle (strict home-cooked diet with no additives, very low fat and semi vegetarian) along with a good couple of hours of physical training/workout a day or should I go and have a natter with the doctor?
A bit of additional information is that even when really going for it exercise-wise my heart rate is always on the low side. I really, really have to try hard to hit 85% MPL...