Back pain is not back pain. There are different causes why back pain occurs and in my opinion there are also different healing methods.
1. Lumbago: Lumbago can happen from one second to the other. One wrong movement and a nerve might not be at the usual place and the pain can begin. Lumbago is painful. There is no way to practice yoga or to do anything. I went to the hospital. There they gave me something to drink. It was a drug that shall relax the muscles. I slept on the aisle in a hotel bed soon after having taken this fluid. After a few hours I was OK again. It was all like a nightmare. I spoke with people who have this lumbago very often.
2. Sacroiliac joint: The hips and the spine is connected via this joint that is rather a gristle. A wrong movement ,i.e. one lifts up a heavy suitcase or one turns around in an awkward manner and something can be blocked there. I got it when I practiced supta kurmasana. I remember when it happened. I thought: Damned, I pulled something. In difference to lumbago the pain can be located almost precisely. It's either on the left or right side of the lower spine.
The recommendation here is to go to the doctor as soon as possible. I postponed this too long. Practicing yoga was not a good idea. But the pain was volatile. During the practice I felt good, but afterwards it was difficult to sit down or to stand up. I could scarcely turn around in bed at night.
The joint got sore. The pills that I got are in general against rheumatic problems. It helped almost at once. After one day I felt so incredible much better.
Today I was in the subway: I could stand up and sit down without pain. A miracle.
Tomorrow I feel ready for my first practice after a break of almost 3 weeks.
3. Back pain in general: I can write only theoretically about it. I think people get back pain if they sit too long in the same position. People who have sedetary jobs might be prone to get back pain, when they don't exercise to balance this life style. Yoga might be very good here, also because it works prophylactic. All sorts of asanas are useful: Standing asanas, forward bending, back bending, twists, inversions .....
For the time being there is a gap between what I want and what is possible. I think it's good advice to start slowly and to focus on the breath.