Even if you meant it, you didn't write: "When I had mental health issues, going back to work ASAP helped me. But, I understand that everyone is different and not all people are able to follow my advice and do the same".
Instead, you wrote "It's about weighing up what is best for you in your situation, what more you may lose by not being in work and comparing against the gains. " - meaning that everyone with mental health issues can "weighing up" what to do, to work or stay home.
It is ignorant to write it and assume that only because you managed to keep working while you had mental health issues, then everyone else can do the same. You don't even acknowledge that some people have it worse than you had and can't follow your advice.
I am talking now from my own experience too, and I know very well how it feels to be able to carry on working despite struggling with mental health issues versus not being able to work at all. It feels terrible either way and has nothing to do with being able to magically "weighing up" to work or not.
OP made it clear from the start that she can't work now because of her mental health issues. There's no reasons for anyone to question her why she doesn't work and give her advice to go back to work, especially if she has a fit note from her GP.
Mental health issues and physical issues are similar, we can't control it. In both cases, all depends on how severe it is. There's nothing worse in this life, than feeling so bad that you can't work because of your own health. It automatically means that you can't enjoy your own life outside work.
It doesn't matter if it's physical issues, mental health issues or both at the same time. It's unfair to judge any person on what kind of body they have and how healthy they are. Because what kind of body and health we have is not our choice, it's something what we were born with and we don't have power to control it.