My Blood Pressure Drops Significantly After Standing Up Straight — Anyone Have Experience with That?

When I go out in public I usually like to stand up straighter than I am at home. Unfortunately, this puts a strain on my body and can affect my breathing. I'm fairly sure it has to do with the lowering of my blood pressure. For example, I was slightly hunched over measuring my blood pressure today and got a reading of 102/76. Then I remained in the same spot and stood up straight and measured my blood pressure. I began having some breathing problems while my blood pressure was being read. When the monitor was done, it was 84/68. This was only one minute later from the previous reading.

Does anyone have any experience with this?