I second this. I don't know why, but I can feel my heart beat at all times. After strenuous exercise, it throbs very forcibly, but it's also very noticeable when lying in bed (I sleep in a prone position). It's not a great feeling, because, for one, it reminds you that you have a thing that's beating all the time and would kill you if it stopped, and also because it's just annoying to be feeling your heart pulsing inside you every moment of the day.
For me it's a lovely piece of mechanical sympathy I can have with my own body: it lets me tell if I'm agitated or soothed in ways I'm not immediately aware of.
