When the headache starts, it comes out of nowhere with a sharp
right where my head meets my neck
on the back lefthand side. The pain is intense but it fades fairly quickly (within a minute). However, for hours afterward, I'll get aftershocks, I guess that's the best way to describe it - it's in the same spot, same feeling, just less severe (still painful).
Like I said, I don't think there's a linking factor.