I have recently started wondering about this.
I have migraine headaches occasionally, sometimes for no reason I can tell. They can come on quick, and my longest has lasted three very long days. Sensitivity to light, nausea, lethargy, and sometimes full up vomiting often accompany the pain, and I even had the lights in my vision once. I have been prescribed Imotrex and that usually works, but even after taking that I feel wiped out.
But, so far I have never had one while hiking. I don't know if it is just luck, or if something about hiking keeps them from happening. I figure someone else here on WhiteBlaze probably has the same problems and I was wondering about your experience.