I have been training for about 15 weeks after several months off. I did my first workout on Monday, a 4 mile tempo run on the track in 27 MINUTES! It was just plain depressing. Worst workout I have ever ran. Nothing went particularly wrong, I ran comfortably hard and when I clicked my watch at the end, I found out how terribly out of shape I actually was.
But THEN, I run another workout today. 4 x 1 mile tempo run ont he track. My splits were 5:33, 5:34, 5:40, 5:39. I didn't check my watch until the 3rd one, and when I saw the time, I thought I skipped a lap. But then I hit a 5:39 on the last one, and I just couldn't believe it.
I still don't get it. Monday was horrendous, Wednesday was miraculous. Regardless, I am pretty happy with my progress now.