New personal distance record

I ran 10.36 miles yesterday. I kind of amazed myself that I was able to run that far without stopping other than to cross at a crosswalk one time. (15 seconds) The more I ran yesterday, the easier it got and the faster I ran. I don't know why, but after mile 6, I started to pick up the pace. And by mile 8-9, I was running an unbelievable pace. Runner's high? I don't know. This is all new to me. If you know what that means, by all means tell me!