It still haunts me?

I couldn't believe that it struck my heart and mind with strong anxiety at that moment. It was the moment I saw a familiar back of someone in a fast food restaurant. For that moment, I thought it was really her and I was contemplating what kind of face expression I should possess? One with a warming smile like one when I see an old friend? Or just pretend as though I didn't see her? Then, I thought maybe I should just stay cool and throw a smile when she looks at me. I was waiting anxiously for her turning over and oh...it wasn't her... So, what was my anxiety all about?Dang...