W9 Bad start

After extending W8R3 to 5K, I wondered whether I could then count two W9 runs as graduating (rather like marking your own homework). Pride goes before etc. and I set out for W9R1 with an extension of the normal route at the beginning, hoping to do another 5k; after precisely 1k, a pain running down over my knee brought me to a halt. Walking for half a dozen paces seemed to be OK but the pain returned shortly after re-starting the run. I repeated this sequence several times before giving up and walking home without any difficulty. Great disappointment since I have had no problems of this type over the months I have been following the programme. The starting section was over paths in urban roads and I find these awkward because of the regular dips at the drive entrances. The last part was down a moderate slope, which creates increased impact. So how long do I wait before trying again? With no problem walking, I don't have a guide.