Not sure how it happened, but the lats just kinda locked up. Sore. Limited mobility. Spasm.
I’m certain that the long term solution is to stretch and strengthen the back muscles and abs, keep weight down, keep good posture, and keep good bending and lifting habits.
How about short term? Just take Advil and rest? Icy Hot? Heat pad? Stretch? Doans?
I tried Google, but all I get is a bunch of people trying to sell me chiropractics and stuff.
What do you do for back pain?
I’m sure you know all the warnings about getting medical advice from well meaning but often ill informed people but here’s my 2¢. I had a back injury that was basically a strained muscle that caused pretty severe pain whenever it spasmed and pinched a nerve. My doc sent me to physical therapy where each session started with a hot pad to relax the muscles prior to stretching. A really long soak in a pad wrapped in a damp towel for most heat. Would put me to sleep half the time. What seemed to do the most good was laying on my back and using my abdominal muscles to force the small of my back flat to the floor as I could get it. Then they’d have me do things like various leg lifts and stretching by wrapping a short strap around my foot so I could hold it above my chest then straightening my knee. It took quite some time to get better but a session of that and I could do a fair bit of walking without pain. YMMV, caveat emptor, if you go and kill yourself don’t come running to and/or sic your lawyers on me, Cecil, Ed or the Chicago Reader.
You can skip the disclaimers in this thread. I will not rely on advice in this thread as reliable medical advice for my particular condition or substitute anything in this thread for the advice of my own physician.
Thank you, and carry on! 
I’ve heard good things about foam rollers with regard to tight muscles. Take a look.