Palpitations can be serious, and what makes this a concern for your father is that he's had high blood pressure for many years. This puts him at risk for congestive
heart failure, hypertrophic cardiomyopathy, and coronary artery disease, all of which can be associated with different types of arrhythmias.
What your father needs is some kind of continuous monitoring ECG: not a single ECG, but monitoring for at least 24 hours or even longer. Sometimes that's done with a cell phone report device, but a 24-hour Holter monitor would probably be the best way to capture what the arrhythmia is. Once your father's doctor has that information, she'll be able to figure out your father's prognosis and what should be done. And given his risk factors, your father also needs to be evaluated for coronary artery disease and for congestive heart failure. This type of symptom is definitely cause for concern, and your father absolutely needs to discuss it with his doctor.