Can someone please explain this?

Whenever I take my blood pressure anything like slouching, talking and moving can raise my blood pressure significantly , like 15-25+ on the systolic and 10-20 on the diastolic. 

My blood pressure ranges from 115-123 over 65-75 but whenever I do anything of the listed above It can be 140/85-90. 

For example this afternoon my blood pressure was 145 over 90 , slouched . The next reading I took with a straight back it immediately drop to 123/79 and the following readings were in that normal ranges as well.

I test this on my girlfriend and sister and their blood pressure did not seem to fluctuate like mines does . 

Is there something going on here ?

Is this normal for blood pressure to fluctuate so greatly just by going from slouching to a straight back?

It would not be surprising to find that a slouching posture impedes some vascular blood flow that correspondingly raises your BP.  After a while, you may justifiably start to wonder if there is anything that you do that doesn't affect ones BP.

 but.......

I think that the best help you can be to your doctor (and their diagnosis & treatment) when you are monitoring your own BP is to keep the posture and times of the monitoring consistent, so that they can get an accurate

base line to work with.

I have just been reading about the link between bad posture and high blood pressure because my blood pressure has spiked recently and I have a head forward posture which I am trying to correct. I found the following research by Professor Jim Deuchars at Leeds University:

https://www.leeds.ac.uk/news/article/340/how_a_pain_in_the_neck_could_be_bad_for_your_blood_pressure

I am learning the Alexander Technique to correct my posture and hopefully it will lower my blood pressure.