It COULD be anxiety and the adrenergic response that is normally associated with fear or anxiety. But really the tell is if there is a discernible arrhythmia as evinced via ECG or loop recorder or by a physician. Also, the pacemakers these days can be polled via Bluetooth and it will show in the record if you have an arrythmia or tachyarrhythmia. If it gets so bad that you can't get around or past this experience, I suggest you visit a clinic or go to an emergency room and see if they can't put your mind at ease.