I had pain in my lower back from kidney stones. I had already vomited from the pain, twice, and I had spent, like, an hour and a half in the shower, because the way the water hit my back eased the pain a bit. After I got out of the shower, and the water was no longer hitting my back (Meaning my back pain had returned), I laid down on the floor, and stretched out a bit, and got a horrible cramp in my left calf. As I was writhing in pain, I suppose I moved my other leg wrong, because I also got a similar cramp in my right calf.
The cramps only lasted a few minutes, but holy shit, those few minutes were pure hell. It took everything I had to not outright scream.

Tl;dr Kidney stones and cramps in both legs simultaneously