After a 10k? It's hard to explain. It feels...refreshing? I think that's a good way to put it. Especially after a run by yourself, there's something about being a small handful of people outside and running at any point in time, just you, and the road or trail in front of you. There's a goal, right? And you're going to meet that goal because otherwise you're walking. At the end you're tired, no doubt, but you feel strong, you feel ready for the next run. I'm not sure if that's a runners high, I do get that during some longer runs, but that's more a feeling of having no thoughts, not even really feeling the motions, but you're going, and going, and going.