Back goes poing!

Is it possible to throw out your back while sleeping? I woke up in the middle of the night when the back muscles under my shoulder suddenly seized up. I had to wake up Chuckro and get him to massage them out a bit because I was having trouble breathing, it hurt so much. Every time I expanded my ribcage, I got a fresh wave of stabbity goodness.

It's still harpstring-tight and painful. I'm moving really gingerly. What the heck, back?