Having to compromise on the career front is really painful, because like you said, we work our arse off to get where we are, and then some T swans in and says, "No, you can't have that, that's not gonna work for you." It's one of those areas where, to the outside world, we still seem 'normal', successful even...v painful.
If you can approach this is a temporary measure, would that help? Like, "I'm going part time for a few months/years to get my health sorted so I can return to this career some day and really kick @rse".
Ultimately your T is right, if you know work in its current form is unsustainable, there's 2 options: bite the bullet and go part time, or do the head in the sand thing and start counting down to the big dramatic breakdown (where you may end up not being able to work at all)...
I went part time for ages and my employer was actually really awesome about it. I never said "PTSD", and my doc was good about just putting "Bipolar" on my medical certs, but my employer basically let me pick my own hours week to week. Colleagues got used to me coming and going really quickly and overall, it was really important to me knowing I was taking as much control of protecting my career as possible. That was actually something positive I was doing for my self, my self worth, and my future. Once I stopped judging myself for not being able to sustain the impossible, it was all up a really good experience (I think colleagues tend to pick up on whether you're feeling vulnerable or self-confident about your altered work schedule).
If you don't want to put PTSD on the table, for most of the workplace all they need to know is that you have some other "personal commitments" that will be demanding a bit of your time for a while (most people assume that's a family thing;) ).
This is a positive step you can take to protect your career. Even though it hurts now and there's the whole negative "how much of a failure am I" thing that our heads do, in the long run, this is probably the choice that best protects your career, despite how it feels right now.
