I Have This Problem When I'm Running...

I have this weird problem when I jog.  When most people jog, people nod at them or wave or say hi or maybe just ignore them.  When I jog, people more often than not say things like "you can make it" or "not much further", like I am about to die or something.  I am not exactly Governor Arnold but I am not John Candy either.  I wish I knew what it was about my body language when I jog that makes everyone think I am about to have a coronary - maybe I will have to get my wife to video me sometime.  Or maybe not - the kids would probably run it over and over and laugh at me.