Struggling with wondering if something is a real memory or not is extremely common and makes a lot of sense. Remember that extreme disassociation serves the very purpose of making something that was too traumatic seem like it never really happened. So I think it is very natural to have moments of wondering, "Am I imagining this?" or "Is my brain making this up?" because the whole point of repressed memories in the first place is to make it "not real" by just completely blocking it out, as if the brain says, "Okay, that never happened!" So when you start to have flashbacks, it makes a lot of sense that parts of your mind might be like, "Wait, thought that never happened?" or "Are you sure this happened?" It's part of the processing, well process. Small steps.