I have no idea and nor does any of the several doctors that I have visited. I also have muscle spasms in my upper back and tingling in my feet and legs. I have had all sorts of test done and nothing is ever found. However, one doctor had me do an MRI and he discovered that I do have a pinched nerve in my neck. I take theraphy 3 times a week for the pinched nerve and it eleviates some of my pain in my upper back. If you should find out more about this pressure in the head please post it here for all of us. There are a lot of people with the same condition that we have. Hang in there and don't give up hope for change to come for us.