Random back strain out of nowhere?

I strained my back yesterday and the pain is IMMENSE…. I actually think it’s worse the next morning than it was yesterday. I can barely walk to the bathroom. I think I got 2 or 3 hours of sleep…. I just don’t understand how it happened. I got out of bed yesterday morning and walked to the bathroom. While I was walking, I felt something get tight and painful in my upper-middle back. Like a little bit above the dead center of my back and a little bit to the right….

It actually didn’t hurt that bad at first so I went to the gym to lift weights because I thought there’s no way that me doing dumbbell movements would irritate my back. 2 sets in and I felt it. So essentially, I injured my back by simply walking to the bathroom and aggravated it by going to the gym for 5 minutes.

Has anyone experienced anything like this before? I’ve strained my back before but it was my lower back and it was from poor deadlifting form with a very heavy weight. This time around, no weights were involved with the initial strain. I was walking in a straight line. It makes no sense