Mine's all muscular. My whole lower back strained and has been clinched tighter than a drum. I can't stand or walk for more than about ten minutes at a time because of it. It's improving though. Next week I should be back to work.
I slept on some nasty hotel mattress. This isn't the first time that's happened. The other times I've injured it were at work lifting heavy stuff that I had no business lifting. I'm on my knees a couple hours per day too so that doesn't help a whole lot.
Take it from an old tile setter. I was going to my Chiropractor twice a week. I bought a Teeter and haven't been back in 7 years. I swear by my Teeter!