Charlie horse of the head

While lying in bed and when I yawn, sometimes I get a charlie horse sensation in my head.  It goes from my neck all the way up one side of my scalp and affects my ear on that side.  It hurts just as a charlie horse does and lasts for a min or so.  Since you 'walk off' a charlie horse for the most part, I try to massage my scalp as best I can to try to relax my neck and scalp.  Can anyone give me an idea of why this happens?

[Caryopteris]

I think it's that the trigeminal nerve gets pinched.  I used to have that when I was a kid, but not anymore.