I get these sometimes too and not sure why did a quick google search and come up w/ this :

http://www.active.com/running/Articles/Post-exercise_headaches.htm

http://health.msn.com/health-topics/pain-management/headaches/articlepage.aspx?cp-documentid=100145776

I usually get them after hard workouts and think somehow it's related to blood pressure I take aspirin or the like and that usually helps. if that doesn't work for you might be worth a visit to the docs

This sometimes happens to me as well, or sometimes a stomach ache occurs. After you run your hard work out MAKE SURE TO WARM DOWN and stretch after. Not warming down could very well be a factor. When I know i've ran hard, I like to lay somewhere flat, like the floor or carpet, and just stare up at the sky or the ceiling. It relaxes the muscles, and mind. This seems to work for me, just to kick my body out of hyperdrive mode, and it seems to help the night-time headaches and stomachaches. Hope i've been of some help

I get MASSIVE headaches after races and hard workouts. I'm definitely well-hydrated, cooled down and fed. My chiropracter thinks it has to do with my head and neck position - I lead a little with my chin while running...A nutritionist thought it might be out of balance electrolytes, so I'm taking calcium and magnesium supplements. I hate taking drugs prophylactically, but that's what it's come to for me - ibuprofin or aspirin right after races...and a little coca cola for caffeine. I also ice my neck and shoulders.

I used to have this problem as well.  I finally realized it was caused by low blood sugar.  Immediately after a workout take in some calories, preferably liquid.  If my workout ends at home I drink a big glass of milk.  Away from home I use Hammer Recoverite.  It is good to have some protein with the carbohydrates.  Don't wait till after your shower, or til you drive home.  The sooner the better.  Give it a try, you have nothing to loose but pain.  I have been exercise headache free for 14 years.

Hello, I have the same problem even with low intensity workouts.

Could you please share your experiments, possibly not the medicines? I am going to try the caffeine. I tried already drinking more but it didn't work.

Thank you!