My blood pressure is normally 120/70.

I started feeling off (lightheaded, heart fluttering) so I took my blood pressure (which hurt, really bad. My hand tingled and the veins popped out a lot) and it was the highest it's ever been for me - 139/79.
I put magnesium spray all over my legs right away and also took my magnesium tablets (that I take for leg cramps) with a bunch of water, and took it again five minutes later and it was down to 135/73.
Just now I tested again and it's 141/89.

Is this cause for concern? Should I be calling my midwife (it's almost midnight, I don't want to call unless I need to)?

I'm 29 weeks pregnant, btw.