so typically I jog to and from poker night. tonight I decided to run back. With half a block to go I noticed headlights from a car behind me (about 2 blocks behind me), and I decide to get on the sidewalk rather than the middle of the road (middle of the road was illuminated by street lights, so I didn't need to worry about kids leaving toys on the sidewalk). Right about this time I get a nice muscle-pull feeling from my sternum to my mid-right side. Right now it hurts to breathe.