What Causes Sudden Pain And Pressure On Right Side Of Eye And Head?

I was coming down a mountain while driving back from San Diego, while enroute I felt a small pressure like pain over my right eye. I attempted to relieve the pressure by pinching my nose and blowing, I then felt a horrible pain on the whole right side of my head, over my eye and in the back of my head for about ten minutes. Worst pain I have felt in a long time. What can this be? Since then the inside of my head has been sore almost like a head ache