What Causes Recurrent Panic Attacks Despite Taking Valium?

I had a severe panic attack today, while shopping in a store that I have frequently visit and love, while on vacation, so there seemed to be no apparent reason for the attack. I have gotten panic attacks but only connected to claustrophobia, so this was completely new. I went outside to catch my breath, I thought I was going to pass out in the store. So it would go away but it kept coming back after I seemed to have recovered --- dizziness, heavy breathing, racing heart, tingling in my arms and fingers, dizzy... this kept happening over the span of the next hour and I thought I was dying. I went to urgent care, they did an EKG, came back fine, gave me 5mg valium, got better, and then panic attacks kept recurring. They sent me by ambulance to hospital, ran tests, all were fine. They gave me script for valium and sent me home. I will follow up with doctor when I get home. Now I am so scared that this will happen again. What do you suggest? Going on an anti-anxiety medication? I am healthy, 43 year old female, run every day and that s how I mitigate my anxiety and depression. But now, I am so fearful this will reoccur. What do you suggest?