There is no "probably" about it. When you feel in danger your body releases adrenaline which immediately increases your heart rate so you can run from the danger.
I had this same fear and its complete nonsense.
The absolute worst thing you can do is monitor / focus on your heart rate numbers.
What is the "cure" for this? Ill tell you what helped me. Depending on how out of shape you are, go for a walk/jog/run, force your heart to pound. You will feel it pounding, but keep going for a few minutes. After you stop your heart will start to normalize and return a normal resting rate (This process always happens even if you have a panic attack).
Do this several times and then you should build some confidence in your heart. This is important because when you are laying in your bed anxiously checking your pulse you can say "This is not a big deal, I walked/jog/ran a mile and my heart was fine".
It's a very strong muscle that has been beating your entire life NON STOP.