What you are seeing is the pulse from your heart beat reflected in the column of blood in your jugular vein, a jugular pulse.
If you are on the thin side, do not have swollen ankles, and are not short of breath, this is probably not of concern. However, I should add that if it is apparent when you are sitting or standing up, you should see your physician as soon as possible.
Now, the fact that it is not associated with each heart beat makes me suspicious that you may have an abnormality of heart rhythm, another reason to see you physician soon.
If you notice the pulsation while lying down or notice any of the things I mentioned above, this can be an emergency and reason to go to an ER.
Let me know if you want to "talk" about this. I teach medicine, so I am not available at all times. However, I do check this site throughout the day. Please be patient; I will reply.