Yes. Yes this is a serious problem, if acutely ill need to go to er, otherwise discuss with your doctor asap.
Depends on rhythm. Many cardiac arrhythmias are benign - abnormal but don't cause any problems; while others are not. First find out what arrhythmia, then ask your doctor for advice. Pacs and rare pvc, may require no treatment, atrial fibrillation may need anti coagulation and possibly cardioversion, VT may need defibrillator. Choice will depend on your medical history, too. See a doctor.
Have an ECG to check. Any type of irregular heart beat is called an arrhythmia and many people have this. Most of the time is not dangerous and simply a skipped beat or a pause. Warning signs are a rapid or racing heart beat that does not stop, or if you feel dizzy or short of breath or like you might faint. This could be a less common but more dangerous arrhythmia. The only way to know is to have an ecg.