Strange heart sensation after almost getting into a car accident?

Hey everyone. I've struggled with heart problems, or so I thought, before. I've had a few ECGs, and ekg, holter monitor, and bloodwork. Nothing has ever shown to be wrong with my heart. For the last few months, when under some stress, I have been experiencing heart flutters and weird adrenaline rushes that make me lose my breathe. I went to the doctors in March and still the doctor said everything was ok. Today my friend was driving and and big truck almost swerved into our lane, I got really scared and I almost "knew" something was going to happen with my heart because i could feel it picking up speed. About 15 seconds after the accident I began to feel this extreme flutter, almost like a quivering, feeling in my chest. This triggered my flight response and I immediately reached for water and told my friend to pull the car over. It was like I didnt have control over my body for the 5 seconds that the fluttering was going on for. I'm thankfully home now, a bit shaken up, but I'm just scared as to what this is. Any idea?