I do 1 hour of cardio every day followed by 1 hour of strength training. I have been doing this since 1/2013 with no issues until about a week ago. The head ach is only on the left side of my head.
Part of the trouble is that if you wait until you get thirsty while you are doing exercises,you're actually too late, and if you drink too much in one go your body won't be able to absorb all of it.
If you really want to treat your body right you should try to drink small gulps frequently, particularly while exercising.
Then again, if you're fully hydrated when you start working out you should be able to go at least one hour before dehydration actually becomes significant.
Thank you I will work on drinking more water practivy to prevent dehydration head achs.