Thanks so much for this. I've been dealing with a lot of upper back and shoulder pain the last few years (also in your age range) and have tried so many things to fix it. I know the problem is being on the computer so much, but I need to be for my work just as you do. I put in frequent breaks, doing some gardening, walking the dog, etc. but stuff needs to get done and a lot of hours are needed to do it.
I love that your advice here doesn't require not sitting, but rather simply sitting without using the back of the chair! I'm sitting here writing this on this fancy ergonomic chair designed to take pressure off as I use it for support, but when I tip my tailbone back as you suggested, I simply cannot get comfortable on this chair.
I realize now that it's because this really isn't an ergonomically correct chair at all. It's just padded a lot to make the pain come on so slowly that you don't notice it until you get up. Now I'm sitting on the front edge of the chair with my tailbone back and immediately feel relief in my shoulder, though I'm noticing tightening in mid-back muscles I don't often use.
I'm going to try to the instructions in the sleeping video tonight. Thanks again for this. You may have just spared me a lot of physical problems. (And I too have been starting to get heart arrhythmia. I had no idea it was connected to posture.)
Nice to find you on here and I look forward to seeing more of your posts. Just followed you.