Do you have any other symptoms, like back pain, neck pain? Have you ever been checked for the anatomical leg length difference?
I would get it checked by good chriopractor or osteopath. Somebody who can measure your posture.
good luck

Hi
There is a good idea to have it checked by a professional.
You may consider visiting a GOOD chiropractor who can assess your posture thoroughly in standing and lying position.
Another option is craniosacral therapy or neuromuscular therapy. I would ask around for an experienced therapist.

You can check: www.upledger.com and www.stjohnseminars.com

It seems like it is muscular because massage gives you the relief, but probably the cause of the problem is somewhere else. That's why evaluating for postural distortions is important.

I probably could write a 10-page essay about it but have no time.
You can find a lot of information on the web.
I only would like to mention some very important reflexes in the body called Righting Reflexes. In a very short version it means that your body will do anything to make your eyes even with a horizon. So, for example if your hips are imbalanced ( for whatever reason) your body will adjust by making changes in other parts of your body to maintain balance ( in your case maybe part of the adjustment is in temporal bones?) . Try to walk for a little bit with your head tilted... probably you will get dizzy.

Take care
Bociak