This happened when I went running today.
I know, you read that correctly, I f.i.n.a.l.l.y. went running again after MONTHS! Nothing like being surrounded by extreme and not so extreme illness for a couple of weeks to get you focused on maintaining your health!
I have indeed discovered a great truth. There is a trick to enjoying running and it is this:
Keep your expectations very very very low. If you go out convinced that you are going to be utterly hopeless and pathetic, you are utterly delighted by anything at all that you do achieve, and you come home with a thrilling sense of your own ability, even if your efforts were kinda sad.
Just keep assuming you're far worse than you could possibly be, and everything else comes as a pleasant surprise.