Your posts remind me so much of myself! It is so hard, this recovery. Doubly hard for people with Anxiety and/or The Depression. I had BTKR the last day of August and I'm only just now starting to enjoy the rewards of going through a ridiculously heinous surgery. I was really starting to get frustrated and very sad right about the 2 month mark.
I was thinking about this... How after a certain point you can be overwhelmed with negative feelings and hopelessness. I have a couple of theories. One is that as we oh so slowly recover, we push ourselves a little more here and there. And it's very easy to overdo something and have your knee rebel. Remember you basically had a bad car accident on purpose. Your actual bones have been drilled into. (OK , maybe don't think about that too much!) Any wrong or too much micromovement can set you back quickly. Then it feels like you have to start all over again. And isn't that depressing?
My other theory is that in life, a most bump in the road type events either resolve or we acclimate in about 2-6 weeks. And there's usually a linear progression. So when you experience a setback in this recovery it can really feel like reality just isn't following the rules. Or that you did something wrong. So you're left with a very unpleasant cognitive dissonance.
So, I'm not saying it's easy. It's not easy. But there are some things you can do to cope. First, don't beat yourself up if you experience a setback after movement. Let yourself have a learning experience and try to be okay with just resting again. That's the hardest thing. But try to think of it as getting another tool in your toolbox on how to treat yourself slowly. Next, tune out, fire, or ignore 'professionals' who stress you out. Clearly, they aren't doing their job if it makes you feel anxious.
Don't over-think things and second guess yourself. The best thing you can do is keep participating in this community. You will always find positive support and excellent information. Most often you'll receive the positive feedback you need to stop second-guessing yourself and trust your own feelings and body. No one understands this like someone who's actually gone through it.
I am very grateful for how far I've come, but I see that this will be a long journey for me. I try to enjoy the new things I can do, like walk without looking like I pooped my pants. But I also try to stay as positive as I can when it gets difficult again. I think back to when maybe just getting to the bathroom unassisted was my biggest accomplishment of the day.
This forum can be a real boost. Just keep posting and reading here and it will help so much.