Random brief sharp pains in left side of neck.followed by head pain.muscle or maybe something serious?

Age and medical hx?: So age and previous medical history will play into the diagnosis here, but if you don't have a previous history, and are relatively young, I would likely chalk this up to muscular. Possibly something suboccipital (base of skull), which may press on one of the nerves running up front along your skull. An osteopathic physician could help with this; muscle relaxants may also help. Good luck!