New chest pains when suddenly scared

I recently was driving and thought I was going to be hit by an oncoming vehicle.  I was very suddenly scared.  When this happened my entire left arm went numb and it almost seemed paralyzed with this feeling slowly wearing off over 30 minutes.  I had chest pain, mostly left side.  I told my doctor about this a few weeks after it happened and she didn’t tell me what it might have been, but sent me for an EKG and wants me to get a stress test and chest x-ray.  I tried to look this up on the Internet, but can’t really find anything about what it might be.  Since then I have had similar sensations again when driving when something happens suddenly and I am faced with potential vehicle accidents.