I visited my doctor today to make sure I didn't do anything serious to the knee. She doesn't think I tore anything but after feeling around the knee thinks the issue is Patellofemoral Syndrome. Here's what it is:
She ordered me to stop doing squats for a while until the knee feels normal again. When I resume squatting she wants me to use reduced weight. This sort of sucks because squatting is a major part of the workout I've been doing. It also sort of sucks because my knee feels funky. I'm going to have to find another workout regimen.
PFS is caused by an abnormality in how the kneecap (patella) slides over the lower end of the thigh bone (the femur). Normally, the patella (kneecap) is pulled up over the end of the femur in a straight line by the quadriceps (thigh) muscle. In PFS, there is patellar "tracking" toward the lateral (outer) side of the femur. This off-kilter path permits the underside of the patella to grate along the femur leading to chronic inflammation and pain.
Upon reading more about Patellofemoral Syndrome I learned it is also called "housemaid's knee" or "secretary's knee." This discovery did not do much for my hope of it being a manly injury.