Feeling good?

Alright, so I'm not as fast as I was last year. So what?
I came in 4 minutes slower at the 18 mile tune up this year than last.
I'd be ok with this "getting slower" crap if I understood why it's happening. My disc isn't the problem. I'm eating what I think I should be eating. I never get enough sleep, but who does and when has that ever been an issue?
I did a good 4 mile speed work out this morning. I'm going to time myself around the 6 mile loop tomorrow...actually, scratch that. Grete's Gallop is two loops around CP, so I'm staying out of the park for the rest of the week. Speaking of, my average pace per mile at Grete's was 9:12. My 18 mile pace last year was 9:35. Over the weekend it was 9:47! OK, so it was incredibly humid and horrible outside, that may have affected me.
If anyone has any theories about why I may be getting slower I am willing to listen.