Today during swim practice we did an especially hard no-breathing swim set. It has been a while since I have done any cardio workout. The last time I swam was a couple months ago during water polo season. Inbetween the seasons I regularly worked out (pushups, pullups etc.) but like I said I didn t do any cardio. During the set I started blacking out and seeing spots but I pushed through and finished. Afterwards my head hurt like crazy but I still went through with practice feeling OK. Now, after practice, I realized that my head still hurts, albeit less than right after the set. What s going on??