Comforting pain

I suffered from DOMS.....ran a 4km on tues but muscle soreness only came on thurs and pain thru friday....so I decided to go for a short 3-4km run on a flat route.....but pain became enjoyable along the way and went on to do the whole 6.3km route with a number of slopes......did a consistent 6min pace...not bad for someone who just started from zero