Measuring my own blood pressure...

When I take my own blood pressure at home, I am convinced I can see my own systolic reading decrease while I measure it and as I relax during the measurement itself. I request a professional opinion on the possible implications of this ‘ghost systolic reading’, specifically when it comes to selecting hypertension drug dosage based on the reading.
I have been using a good quality manual sphygmomanometer and stethoscope for many years. I inflate the cuff to 150mmHg and then slowly release pressure on the cuff valve. Once I detect the initial systolic reading (thumping in the stethoscope), I immediately close the air valve and hold the systolic pressure for a few seconds while I relax. Once the thumping has ceased, I re-open the air valve and allow air to bleed while watching the reading. Soon the thumping returns at a lower valve, typically 10-20mmHg below the initial systolic reading. Then, I continue to release air until I get the diastolic pressure.