What you are describing sounds like it fits with a dissociative type experience to me. If I am understanding you right, it sounds like when you encounter a trigger that connects with something from your past you then find yourself in a completely different emotional space that connects only to a whole lot of negative experience, emotion and memory.
Is that what you are describing? Like there is a 'normal' you who can be clear headed and functional in the world, but when something triggers you you experience yourself distinctly differently. Like you find yourself in a very dark/angry/hurting/hopeless/pain-filled place?
And from what you wrote it sounds like when you connect more to those parts of yourself they don't *want* you to get clear-headed again because that means they will be forgotten and pushed aside? But you need to get back to being clear headed so you can function?