Adrenaline causing heart rate to skyrocket! Please help?!

So sometimes when I am doing something like a workout or have already done something that may raise my heart rate naturally, I get this weird scared anxiety fight or flight feeling, that then causes the normal elevated heart rate from the workout to go even higher. One day during a workout my heart rate was at 140 which is good, when all of a sudden I started panicking really bad over the sensation, causing it to go from 140 to 204. Has anyone experienced this extra adrenaline heart rate surge at times when heart rate is already elevated? I am also talking with doctors and having tests to make sure its nothing else, but its only happened during these weird fight or flight moments.