Abnormal blood pressure today. Happen?

I'm 28 and overweight (about 100lbs), but have been on a diet for a month now and losing a good amount of weight so far. Last week I finally went to see the doc and she wanted me to monitor my blood pressure this week for our next appointment on Monday. She said it was high during our appointment but could have just been anxiety so she wanted to be sure (I do have general anxiety disorder). All week my blood pressure 2x a day had been between 125-140/80-90 or so which was lower than what she recorded and told me to be wary of. Then randomly today, it went up to 165/101 in my left arm only. I recorded my right arm and it was actually at 138/80. 10 mins later, I stood up and checked left arm again and it was at 149/98. I did have coffee 2 hours prior but I thought that would have been enough time to pass. Of course now I have anxiety over it all because I'm a bit of a hypochondriac due to my anxiety disorder. Any reasoning why this could happen? Thanks!