Hernia? Followup Note
Nah, it wasn't a hernia. I have apparently developed a hydrocele or some similar thing. Whatever it is, it's not harmful or even painful (anymore -- tho it was for a few days). I have been unicycling again since a couple days after my scare, and that's been fine. I'll just have to keep an eye on this lump I have to make sure it doesn't change. Maybe one day I'll have it removed. For now it's not causing a problem.