I hope it's okay to post something that is second hand, that is, I am suggesting it because someone very close to me has DID, but I don't have it myself.

It sounds a bit like you had walls up when you were talking to your T and had no sense of the others whom you usually hear. A wall could be thought of as a partition that temporarily blocks the view and hearing of all others in the car. Perhaps you could think of it like the little window in between the driver and passengers in a limo; if you can't hear anyone in the back seat then the window is closed. A wall is up.

Meanwhile perhaps there was a part who was still with you in the front seat who was helping you, giving you this no-nonsense strength to talk openly?

If a part is able to come out and put up walls, I think that's one way others may wind up in the trunk / boot. This might happen if a protector part feels something might happen that others can't or shouldn't have to deal with.

I think there is tremendous variability in how these internal systems are arranged, but often the inner people have been aware of the multiplicity for a long time but the primary or original person (if that exists for a given system) was the one who was kept in the dark for a long time. I think I'm probably talking about highly dissociated systems here. If it's possible, asking the inner parts to simply explain the system to you might be quite helpful. Inner children have been around for many years and often have a lot of understanding, though the lingo they use will be of their own invention, rather than being about parts, alters, and car analogies.