Hello. Thank you for your question and welcome to HCM. I carefully read your query. These may be normal and benign phenomena of extrasystoles (heart beats generated from an ectopic focus and not from the normal and natural pacemaker of the heart, the sinus node). If they are present in more than 10.000 times during a day, then they are a cause for treatment for suppressing and preventing them. The episode in your sleep probably is from the rapid eye movement (REM) phase of sleep, when a flush of adrenalin and noradrenalin happens in the system. This is accompanied with an increased heart rate. It is normal for anyone to have extrasystoles during sleep ( nightmare heart beat , some colleagues call them). If there were four consecutive extrasystoles, then this is indicative of a run rhythm of ventricular tachycardia, so proper treatment should be installed, adding your age and strong familial history of sudden cardiac death. Besides treatment, an echocardiogram should be performed, and heart muscle should be evaluated to see if there is any thickening of the heart muscle in a certain area (hypertrophic cardiomyopathy). Although, this is not definitive, my opinion is that you should consult your cardiologist, regarding the above mentioned treatment and test. I hope I have been of help. Wish you a good health. My regards, Dr. Meriton