If you have a normal physical exam, good exercise tolerance and a normal EKG, it would be very unlikely to have structural heart disease (a weak or too thick heart, or a valve problem). An echocardiogram could be obtained, if there is any concern about the potential for you having a structural problem with your heart.
The important thing would be to correlate your symptoms with your heart rhythm. If you have symptoms every night, the Holter monitor should have picked it up. If you did not have any symptoms the night you were being monitored, then an event monitor or another Holter monitor would be in order.
Generally, symptoms like yours are from extra beats (PVC's or PAC's, premature ventricular or atrial contractions) which cause some pauses and strong heart beats. Everyone has them, not every one feels them. I am very sensitive and aware of irregularities in my heart beats. I understand the feeling, but I know it is not dangerous. Sometimes symptoms are from just a strong normal heart beat (which can occasionally be caused by an overactive thyroid), and there are a variety of different types of rapid heart beats that can cause symptoms, and can be suppressed, if needed.
I worry that you feel exhausted. Sleep disorders, metabolic problems such as anemia or thyroid problems, need to be ruled out. Work with your health care team. You will get to the bottom of this problem.