I know this feeling. And it even happened twice to me that my T forgot about an appointment... and believe it or not but it helped so much. I felt forgotten, not important enough, abandoned,... But after a while I realized that this state of panic couldn't continue and found a way out of it. I was a bit like 'If you forget about me, I won't be here waiting for you... this is me-time!'. ;-)
It feels like the worst thing that could happen to you and suddenly it happens and you have to find a way to deal with it. And probably you would too. There's no choice. Of course I definitely don't wish for you that you ever experience the same, but maybe you could ask yourself this 'what if...' question and try to work with that answer with your T.

If it would happen it would still be devastating. You can't really prepare for it even if you torture yourself with that thought and even though it always is a possibility. But you can try to find a strategy that you can use in case it would happen, so that you know you have the power to get through that moment. And I hope you find these tools inside yourself. I think it's important to talk about it and make it all feel a little safer for you.