I had frozen shoulder about 2 years ago and mine was caused by stress. Here's how it happens in a nutshell: Stress causes mineral levels to deplete. When calcium gets too low, the body starts pulling it from the bones and teeth. Calcium levels can then skyrocket, which mine did. The extra calcium sometimes gets deposited on the bone joints (bone spurs, etc.) and because the edges are rough, the normal use of the joint can cause the muscle to tear. I had a full-thickness muscle tear. Frozen shoulder is VERY painful, especially at night and the pain can radiate down the arm and into the hand. At its worst, I could move my arm maybe 3" at most forward from my hip. That was it!
Here's what you do if you find yourself in this unfortunate situation. #1, improve your nutrition by eating plenty of raw fruits & vegetables & chew very thoroughly. #2 immobility will cause stiffness and atrophy, so even though it hurts (yes, I know it does!) start moving that arm. Exercise it every day. You can use a yardstick to help. (You can also toss a rope or belt over an overhead bar and use one hand to pull the other one straight up, a little further each time.) Hold the stick in both hands and use the good arm to help you move the frozen arm. Try to do side to side motions, circles, raise up over your head, etc. Walk your fingers up the wall. You won't get very far at first, but keep at it. See a GOOD massage therapist if you can afford it. Despite what the doctors may tell you, YOU CAN GET FULL USE OF YOUR ARM BACK if you work at it. Don't settle for anything less than full use. It took me a year, but I did it and the pain and effort was worth it, and I could have done it sooner if I had known then what I know now. Another thing you can do is to use hot/cold hydrotherapy on your shoulder. In the shower, run water as hot as you can stand it on your shoulder for 15-20 seconds, then switch to as cold as you can stand it for another 15-20 seconds. Repeat five or six times. (If you need to yell, feel free to do so. It may help!) Oh, I almost forgot...do what you can to get rid of the stress that caused it even if it means finding a different job or whatever. Stress will kill you. If your case was caused by something else, do what you can to eliminate that cause.
Hope this helps someone.