Manda something simular happened to me. not in the exact way it happened to you but the type of alter was the same. heres what happened to me, maybe my situation can help you somehow..one day I was with a friend of mine at the Dairy Queen. We were having a great time socializing and then the next thing I know I had tears on my face and my friend was trying to calm me down. she told me out of no where it seemed I put my head down on the table and started crying. she couldnt get me to stop. Through therapy I came to understand that memories dont always have to be literally something I went through. This memory that my alter was holding was a Feeling. When I was a child my parents took me someplace where I started feeling scared and trapped all the people I was seeing around me that I didnt know. I couldnt leave when I started feeling trapped because I was too young to drive the car out of there. I had to wait until my parents finished their shopping. So in my mind that feeling of being trapped and held captive became a dissociated memory of being trapped/held captive by faceless people that were towering over me on all sides. Once I understood that memories can also be feelings it was easy forme to understand why I had dissociated into this alter that held my memory of feeling trapped and held captive. I explained to my friend that knew I was dissociative, about the alter being a feeling containing alter and if the situation came up again when I was socializing and I needed her help, what I needed was probably for her to just reinforce the fact that, that situation is over and in the past, that I was now safe and it was ok for me to take care of how I am feeling. Thank her for letting me know how we all were feeling but now it was my job to take care of me when I feel like I am trapped and held captive. Over time that alter realized everything was ok and the two of us became one working together.