This is such great information. I recently started sleeping almost sitting up. It seems that if I don't allow a pressure to build up in my ear, it helps with the thumping. And you are right. It is so fast, it was no where near the beat of my heart. I thought I was hearing all four chambers beat. My husband told me that wasn't possible - I believe him.
I appreciate your sharing your information. I must say that I can sleep on either side of my head and no thumping, as long as I am sleeping upright. I am OK with that. It is so much better than waking up nervous from this rapid thumping. I do still feel pressure in my ear. The ENT and GP both see no physical fluid, but there is definitely pressure there to me. I appreciate all the support. I am seeing one more ENT next week. Hopefully I will have similar response - that it is nothing major to worry about. In the meantime I have started addressing salty foods and stress. My family doctor did ask that I lose a few pounds and add more fruits and veggies to my diet. (My BP was a little higher than I have ever had. She attributes it to stress from work and diet.)