This is actually something I see frequently, especially in people who sit at desks in front of computers a lot. When the vertebrae in your neck are not moving properly and become stuck, it basically throws off the proprioceptive input that goes to your brain.
This, along with the associated poor posture causes the muscles in your neck to tighten and cause pain. You may or may not feel the pain in your neck, but you are mainly feeling it in your head.
I would suggest seeing a doctor of chiropractic to see if this is something that can get cleared away without drugs or surgery. Good luck, let me know how it turns out!
Antonio Marotta, D.C.