Suffice it to say, I didn't run the next day. Nor the day after that. On the third day, I was able to walk without any knee pain, and so I tried giving a "gentle jog" a try. However, I had to abort that effort within the first minute, as the pain returned! (An upside to this ordeal was that my shameful trek back home was now only around 2 hundred yards.)
After some googling, I discovered that I suffered from what's known as Iliotibial Band (ITB for short) Syndrome. I looked up the commonly recommended remedies that I can find on the web, e.g. stretching, foam rollers, knee wraps. For several weeks I cross-trained by doing repeats of power walking up steep hills, hoping that, eventually, my knee would heal enough to allow me to do what I really wanted: to run.
During this time I also learned that my ITB syndrome might be due to my poor running form, in particular, running with a "heel strike" landing with each stride. What is more, it became increasingly obvious to me that the running shoe that I was using - with its typical raised, cushiony heel - might be contributing to my heel striking gait. A diatribe against the standard running shoe was a theme in the book that sparked my passion for running, Born to Run, but it seemed relatively minor to me - being overshadowed by a much more important theme of the book, i.e. recapturing the joy of running as a natural way to move - until I saw a connection between my own injury and the type of shoes I was wearing.
Within a week of my research into these issues, I got rid of my old pair of shoes. (Some lucky homeless guy in downtown State Street became its new proud owner!) As many websites I've read suggested, I decided to transition to a more "minimalist" style shoe. (I was not ready to ditch running shoes just yet!) I believed that with a pair of shoes that had a lower heel-to-toe rise, and no motion control / stability features, for example, I could correct my running gait and, ultimately, to run free of injuries. Hopeful thoughts began to fill my mind: "I will give this another shot. I can rebuild. I can, and will, run again. I just need the right shoes!"