I recently get a headache during intense crossfit sessions. I have recently had the flu and while i feel better there is still a lot of snot in my nose and chest. The headached is on the left side of the base of my skull where it meets the spine . It seems to be attached to the back of my left eye and come on quickly with a sharp pain under exertion. It depletes my will very quickly but I usually just wait for it to subside then only exert myself to where the level of pain is bearable. Why and what can I do?: