during exercise my heart will go into hyperdrive then skip several beats in a row i can count to 5 before it restarts. this has happened to me a few times over the years. typically i am exercising and my heart rate will increase very rapidly for a few moments. suddenly it will stop pounding and i cannot feel my pulse and my hr monitor shows 0 for a few seconds. i will get dizzy and sit down but then it starts up again like normal. i am 28 healthy and fit with no history of any health issues. i have mentioned it to my doctor but she just said "huh thats weird" and said to get it checked if it happens more.
i recommend getting it checked out. sometimes getting a second doctor's (or even third's) opinion is great! i had a health issue and i went to multiple doctors before any of them figured it out. you know your body best and you know when something needs to be figured out!