Hi Granite, that is a really scary dream. I am sorry you had to experience that.
If you are experiencing a lot of anxiety about going back to T, that could certainly explain it. It could be that you expect to experience emotional pain and turmoil while you are there. It could also be that a part of yourself doesn't want to go, so is trying to scare you away from her office.
I think it is really interesting that your own chair showed up there, and the chair was safe to sit in. Maybe when you go, you could take something from home with you to help you feel safe? You could take a pillow or pillowcase to sit on, or bring something small you could hide in your purse or pocket if you wanted it to be private.
I often have very vivid nightmares which leave me feeling exhausted when I wake. I hope this dream will leave you alone from now on!