I used to be almost disabled because of back pain. I don’t know the exact cause because as I am from the US, I do not have any access to medical care unless I exit the borders. At the time I went to a free university clinic where they only treated some symptoms and I had to find a solution myself. I finally found online some new diagnosis (a dozen years ago) by one of the top doctors in the world in the field as something he identified as “upper cross syndrome”.
The problem was posture, something I had developed a long time while working in an “properly ergonomic” office but not sure of the exact cause. I have through my own effort gotten better, but still will quickly develop pain (and eventually disability) if I sit too long, if I look down at a smartphone, or if I use a laptop in the way everyone typically does.
Laptops are horribly designed ergonomically. Phones are worse. The problem is the distance between where your hands are and the screen is too small. On a laptop that’s only a few centimeters and on a phone your hands are on the screen so the distance is zero. Ideally, your hands should be at waist level and the screen should be just below eye level.
The solution I use now is weird, but I lay down on my back and hold my laptop upright against my knee by crossing my ankle over my other bent knee. The other option is to use an external monitor (such as in an office) but I find that cumbersome and tiring for more than a few hours. Yes these solutions may sound weird but you know I would say my back is healthier than most people now, compared to how I was before when I was almost disabled.