Deliberately and immediately raising or lowering my Bp

I'm twenty years old and been told I have high blood pressure, After being asked to check it at home, I did it immediately after a stressful situation and it was 150/111, i sat there a few mins and checked it again and it was down to about 124/84. After playing around I realised just by sitting and thinking i can both raise and lower it quite substantially... is this normal?! Thanks