There are some feeling we often fail to describe. Rubatosis is one such word. It is awareness of your own heartbeat.

"The unsettling awareness of your own heartbeat, whose tenuous muscular throbbing feels less like a metronome than a nervous ditty your heart is tapping to itself, the kind that people compulsively hum or sing while walking in complete darkness, as if to casually remind the outside world, I’m here, I’m here, I’m here." - Dictionary of obscure sorrows