Went Running Big Struggle

Whoa what a weird run today. I struggled running for 30 minutes (plus a 5 min cooldown) on the treadmill today. Burned over 600 calories but had a really hard time of it. Incline was set at 2.5 and averaged 5.4 MPH. Six months ago that would have been nothing. Kind of feel bad that it was so hard to run. I did run it all the way though, I was tempted to lower the incline or speed, I kept telling myself, just one more minute, but I did make it to the end.