I have been feeling heartbeat or pulse while lying down on pillow. I mostly feel this eathier in side of neck or back of head. I have this from 3 months. I had ecg and echo and both were normal. ecg only showed sinus tachycardia. I also had thyroid test done which was normal. I have no other symptoms. The bp was also normal. It only happens if I lie down. What to do next. I had covid 9 months back but that long time now.