I have the same problem with tension in my neck. I have been diagnosed with cervical degenerative disc disease. The MRI also stated that I have some reversal of the lordosis. (Which is basically when the spine starts to curve in the wrong direction) When doing research on the reversed lordosis, I read that it can cause tension in the head and neck along with a stiff neck. The disc degeneration is basically a breakdown of the discs within the verterbrae. Turns out that it sounds a lot more serious than what it is.
However, with all that said, that tension sure is aggravating isn't it? Mine is more like a constant pressure and it feels like I got the weight of two heads sometimes. (A slight exaggeration) The doctor recommended physical therapy. I only went twice. Both times they gave me a bit of manual massage along with electrical stimulation using a machine called a TENS unit. Stands for transcutaneous electrical nerve stimulator. Just a complicated name for a massage not given with the human hand. I felt so good that night when I went home. For some reason the second time didn't seem to work as well, but a different person placed the nodes on my neck/back so maybe that made a difference. I am convinced however that I will invest in one of these machines myself rather than spending the time and the money on a physical therapist. The current is extremely low and I don't think you can actually harm yourself so I'm going to try it. You can get them online or through certain medical equipment suppliers. You may need a prescription though.
If you can, get an Xray of your neck (cheaper than an MRI), it will show the degeneration if this is your problem. I don't know how old you are, but I'm only 44, so it can happen at any age.
