I have had things like that happen to me so many times in therapy, too. Looking back are you able to pinpoint what the trigger was and what it meant for you? Finding out what triggered a particular reaction and why helps us to better deal with it the next time it happens.

Structural dissociation tells us that the ANP (apparently normal personality) deals with everyday stuff and is trigger avoidant, but the EP/s (emotional parts) are hypervigilant and constantly on the alert for potential threats, abandonment or abuse. When they 'spot' something the person experiences the trigger state that you described.
Do you think it might have been something about your t's comments that some part of you (Willow?) perceived as a potential threat, abandonment or abuse?