I sometimes get a terrible headache a few hours after my bikeride. First I thought it was due to dehydration, so I use an extra water bottle. That didn't do it, the headaches continued. Then I thought it could be a 'mineral deficiency' (salt/magnesium?) so I fill my water bottles with a mixture of water, lemonade and salt now and take some extra magnesium. I hoped that was it, especially because I didn't experience any headaches for the week after! However, last monday the headache started during my ride already and ended up in something close to a migraine. I think my bike fit is good, my helmet isn't too tight etc. Anyone have a clue what could be the issue?