ah...
mine only happens if i do triceps work out. especially the cable pulldown(not sure if its the correct term). I will get headache and mostly last for a day or two. Unless i take my pain killer which i am avoiding them this year.(it will halt muscle growth)
xray showed that i my neck bone got small small thorns-like thing which is poking the veins.

(Previously, whenever i scold people, i make out(sex), i will get headache till black out. )