I am so sorry about your "BAM" this morning. That has happened to me so many times. I call it "the light switch effect", as it comes on as quickly as flipping a light switch. Sometimes I am aware of a trigger that causes it, and the trigger is usually always really minor, but often times I have no idea what causes it. It is my understanding that not being aware of a trigger, is often the case.
Anyway, you are not alone with your "BAMS".
The best thing that you can do is to accept it, meaning accept your anxiety symptoms, and do your best to go right on with your day.
As always, the very best to you, Kissa!... Chuck