5K slow and hills

Went out in the morning for the usual slow 5K with Natasha. In the afternoon I went back to Chesters Road with the intention of doing five reps, but I was too wiped out after the fourth to do anything except stagger back to the car. My times were 64-65-66-66 - my slowest time today was equal to my previous best time. I may be getting fitter or just better at running up Chesters Road. I suppose my goal would have to be either to run sub-60 or to complete the five which I always fail to do.