What Causes Pain And Pressure In The Head While Dreaming?

Sometimes while i am dreaming, I will starting experiencing the worse pain & pressure in my head and i can t tell if it is real or if i am just dreaming. This is not a headache or anything of the sort. It is a throbing pain as if my brain is expanding and contracting and is just getting ready to explode. In the dream, i feel alot of pain and pressure in my head and i start screaming....and then i wake up. The only thing that scares me is that when i wake up, i actually feel no pain in my head. It s nothing like when i m dreaming...but this leads me to believe that the pain that i feel is happening for real, and not just in my dreams. It s kind of like a aftershock. I don t know what to think.