I've only felt a "runner's high" a few times before today, and never twice in one day. It's when the world disappears, your vision goes a little fuzzy around the edge, pain disappears, and it's just you and your feet hitting the pavement. I felt it today running 4 miles at a blistering 9:09/mile, thankyouverymuch, for which I'm sure I will pay tomorrow. But I also felt something like it while riding Fender. And it was amazing.