WORK-OUT HARDER. if you don't sweat. you didn't try hard enough. if you aren't panting. you didn't try hard enough. if you don't feel like you did a good job. YOU DIDN'T TRY HARD ENOUGH. if you are going to work out, at least make it worth it!
I'm by no means a runner - I have avoided it like the plague in most cases. But occasionally I feel like running just because I can. There will come a day when this body just can't do the things it used to. Live life while you are able to.