I have rheumatoid arthritis and fibromyalgia. The RA has been progressively worse this year, and we haven't found a treatment to work yet. And I've met many writers with fibro. Even if you don't have a chronic disease, writing can be hard on your body.
Did you know sitting is now being considered as dangerous to your health as smoking? And what do we as writers do? We sit. A lot. Because the only thing that gets books written is BIC time. Butt in chair time.
The good news is there are a few things we can do. Diana mentioned the standing desk. I got one too. I use a gel kitchen mat when I'm standing. And when I'm sitting I often use an exercise ball like this. Amazon link.
I started with an exercise ball back when I worked in publishing. The ball requires you to engage your core so you might need to work up to it. Also be careful you don't turn to get something and end up rolling yourself in the floor. They make exercise ball chairs now, too, that solve this problem. My problem, once I moved my office home, was that the kids would take off with it. They thought it was fun.
You are the biggest investment you have in your career. It makes sense to take good care of yourself. I regularly do yoga to help with fibro pain and maintain strength, balance, and flexibility. I eat low carb, gluten free, and as organic and unprocessed as I can. I got my hormones regulated so I can sleep well. All of those have added up. But everyone is different ,and it takes some time to chase down what you need to do to be your best self. But everyone can spend time in nature, getting fresh air, and listening to God.
Be the writer God created you to be.