I have tinnitis, which creates a high pitched whine I can "hear". The beating of my heart changes the pitch of the whine, so I can "hear" my pulse/heartbeat. It can be distracting as I tend to "tune in" on it, and am overly anxious about the rate, rhythm, and intensity. You may have tinnitis as well (I've had it for years, but only fairly recently have I been aware of the heartbeat). If so, that may be the cause.
Sounds to me like High Blood Pressure. THIS can be serious. It can cause a brain aneurism, heart attack or kidney disease if it goes untreated. I have it and when mine is high, I can feel my pulse everywhere. Go get checked out. It is easy to treat!!!! and it must be treated!!!!
Cindy
THE ONLY TIME I FELT A HEART BEAT IN MY HEAD WAS WHEN MY THYROID WENT OVERACTIVE, IT MAY NOT HAVE ANYTHING TO DO WITH YOUR THYROID BUT ITS WORTH CHECKING IT OUT, HAVE YOUR ENERGY LEVELS CHANGED, ANY HAIR OR SKINS CHANGES, HAVE YOU LOST WEIGHT WITHOUT DIETING
HOPE THIS HELPS ABIT