(no subject)

I've done three miles (mostly at 3mph) on the treadmill so far, today. However, I continue to get a headache, which has never happened before in my life from walking, that I recall. It comes on faster if I walk faster (I started out at 4mph and was unhappy before I'd gone a half mile), and only slacks off if I slow down to a ridiculously boring pace. It feels to me as if I need to get more oxygen, but breathing as deep as I can seems to make no difference while I'm walking. (I do think it helps after I stop.) My current hypothesis is that it's my blood pressure going up, and maybe deep, measured breathing after I stop helps it drop back down. Any thoughts?