What Causes Acute Head Pulsation?

Hi, I have a pronounced pulsing behind the top of my ear on the side of my head, just where the ear attaches to the head. This is now lower near the jawbone but behind the upper ear lobe. My pulse is about 80. This is pulsing about 5 times faster. When I lie on my left side at night it is very noticeable. Any idea what this is? Thanks.