I had the same thing happen to me on my last Dr.'s visit. The nurse took my bp while we were chatting so I forgot to ask what it was. She started hooking me up to take it again about 10 minutes later. I asked when they started taking bp twice on the same visit and she told me that the first reading was extraordinarily high. The second reading was much lower and closer to normal for me.

I second the idea to monitor your bp at home for awhile to see what it's doing under normal circumstances.