Age is a bitch! That could be a reason. But really, there are other explanations too.
Years ago, and this is true, I was cleaning my bathtub when suddenly, when I bent my body left to get to the drain, my back seized. I fell over like a bug on its back. I could not roll over or even move. I lay on the cold bathroom floor in November and cried while I laughed at myself. I wrote about this experience and told it to anyone who likes (or does not) to listen to my stories. It's a reoccurring theme because my damn back keeps slipping out of place.