I second 'Don't panic'. Don't forget that just because you've seen a number on the scales, nothing at all has changed in any sense, since the moment before you weighed yourself. And all that's happened since then is that you've started beating the crap out of yourself, mentally. That's a trauma symptom.
The weight gain was also a trauma symptom, if I've understood you correctly?
Do you really want to traumatise yourself for having psychological symptoms of trauma?
If you want to lose weight, start. It's not in any way insurmountable. Just do a bit tomorrow (smaller portions, cut out a snack, go for a walk, manageable stuff), and allow yourself to feel you've started the process of recovery.
I think that recognising where you're at is a big step. I advise people on debt, and opening all the post they've been shoving in a drawer for years is TERRIFYING for them. But, it's how they get to the bit where they work out a solution. It's a forward step. You are stepping forward, too.