I'm on the mend and almost normal again. It was nowhere near as quick as I'd hoped two weeks ago. There are still twinges in my lower back, but I've walked unassisted for the last ten days. There have been knee issues, but I can also twist and turn as necessary. I'm calling it full movement restored and going for a short hooping sesssion this evening.
I still don't know what caused it, but for the next couple months, I'm going to lay off of the strength training and mat pilates. I'll use my hoops to tone, and some basic yoga poses to stretch, but I won't do anything that causes stress on my back.
Even for cardio, I think I might stick with the hoops for at least a week and then jump back into riding the bike. I'm wary, but I'm eager, so here's to getting back in the saddle!
100 miles and counting!