What is wrong if when you lie down you can hear in your ears the sound of your heart beating bang bang bang very loudly?

I'm not aware of this being a symptom of high blood pressure, but it is a typical symptom of a blocked or bent Eustachian Tube. It could be blocked due to an infection or a congenital defect. One treatment for the latter condition is insertion of a stint to straighten the tube. This IS very common and I've heard many people complain of this. It's almost like an echo chamber. I've had it several times in my life as others have and although annoying it does go away. I've had my heart checked out several times and everything is just OK. If you are upset about it see your doctor and they will explain more to you and why this happens.