Agreed, I often get runners high although the intensity varies quite a lot. Best one was at the Preston guild marathon in 2012. I've run 5 marathons and usually suffered having hit the wall at the 22 mile mark. At Preston though I went through 23 miles feeling good and waiting for the expected crash which did not happen. It was pissing with rain, cold, my nipples were bleeding but the last 3 miles were incredible, felt like floating and running faster and faster. Finished just outside the good for age time of 3.15. Biggest buzz ever, apart from Augeroooooo the same year!