How can I combat anxiety during pre-yoga breathing exercises?

I have found some similar(ish) questions online, but none seem to match exactly what has been happening to me. I started taking yoga classes this year about once a week/every two weeks. I think it was my 3rd class that this first happened, and has happened almost every time since (just much less intense than the initial attack): when we begin the class, we are seated legs crossed and close our eyes and "turn our focus inward" and began about a 2-5 minute long breathing exercise. As we are supposed to be clearing our minds, my heart kicks up out of nowhere and begins racing. No matter how hard I try to ignore it and focus on my breathing, I feel this anxiety quickly spreading through me. I begin fidgeting slightly, trying not to bring attention to myself (even though everyone's eyes are supposed to be shut), and usually find brief relief when I open my eyes. As soon as we go into the first position, the anxiety quickly melts and the rest of the class I am fine. The first time it happened, it was so intense I almost got up and left! I'm embarrassed to ask the teacher, and I want to continue my practice; but how do I get past these random mini-panic attacks?