Congrats on your successful surgery. Don't be discouraged or let anxiety get the better of you. Given your history of bypass surgery, it might not be a bad idea to give your Dr's office a call to let them know you have been experiencing. I feel confident that they might want you to come in for an EKG just to check things out.
Secondly, any amount of stress, even if you perceive it to be minimal, can increase symptoms.
Just give his/her office a call...you can only benefit by putting your mind to rest:)
I guess a missed beat hear and there every time I take my pulse (you didn't say that) would cause me to talk with a doctor to see about getting an EKG or other tests to see how the heat wave looks.
If you have a missed beat only sometimes when you check you pulse and you don't notice any missed beat unless you are taking you pulse, I'd not take any immediate action.
You mention anxiety and panic, so if the missed beat makes you more anxious and or worried/panic, I'd get it checked. You don't need any extra stimulation of anxiety/panic problems.