It seems to me that there are two factors at play here.... low pulse probably due to BP medication.... and anxiety.... a pulse of 40-50 without ight headedness or fainting is low but not causing any problems. I always start new bp medication by taking half of the prescribed dosage to make sure my pressure and pulse don't drop to fast. hope this helps.
There is a chance that your high blood pressure is causing a slow heart rhythm. If your blood pressure is too high, the body can respond by slowing the heart rate in order to reduce blood pressure. Just a theory, of course, and there may be other explainations, but usually the heart rate will increase with panic. The heart rate is usually slow at night.
You may also have runs of bigeminy, that every second heart beat is a PVC or a PAC.
What you should have done, was to get an EKG registered when your heart rate was slow. If your heart rate is still slow, I assume you have told your doctor today.
Some blood pressure medicines may slow the heart rate (beta blockers or some calcium channel blockers). I didn't think doctors prescribed those to people with slow heart rate, but I guess anything is possible..