Trauma memories are stored in a different way than normal memories, no matter how painful or intense those memories might be. Trauma memories, once we are able to access them, can feel freakish and unreal. Because trauma is by definition an overwhelming experience, a part of you that experienced the trauma can be stored in a way that has been severed from the rest of you. The experience was so overwhelming, horrific, or terrifying, that you literally "disown" it in order to keep living with yourself, to stay safe and survive.
During trauma, the brain switches into a different mode than when recording normal memories. A non-verbal, non-logical mode. The memories might be stored as visual pieces (as opposed to a full, complete picture), as physical sensations, or both, but they don't have a slot in the normal time sequence of your life. They are kept separate. They remain in the short-term memory, not the long-term memory where your normal experiences go. When trauma memories are triggered by a sight or sound or smell that might actually be benign (and you don't even have to be aware of the specific memory for this to happen, it can be hidden and inaccessible to you), trauma victims can feel like the trauma is literally happening again in the present. They can curl up in actual physical pain, experience heart-pounding adrenaline, hear sounds and see sights, or bolt and run, when the danger is actually long past.
Supposedly the goal of trauma work is to move these crazy-feeling trauma memory pieces in with the normal long term memories, so they can take their rightful place in the timeline. So they no longer feel immediate, but are in the past where they belong. And so you don't feel, well, crazy. In the process of EMDR and trauma work, I keep asking, how long does this take? Because to be honest, I function pretty darn well fragmented. That's how I know how to do life. I'm pretty skilled at distracting myself, at shutting out the dark traumatic stuff (at least in the daytime!), and at simply not thinking about it, keeping it separate. Yes it constricts my life as I do a dance around the various "normal" things that trigger the dark stuff for me. But in general, living fragmented works.
It is possible to be so fragmented you actually don't know things about yourself. It used to be this way for me. Vital information was missing, and there were things in my life that didn't add up. I had crazy reactions to seemingly random things that didn't make sense. Life can feel surreal then. And lonely. Nobody knows the real you. It is possible to be disconnected, divided on the inside, even from yourself. I imagine that for people who don't have traumatic memories, this does not make much sense. But for those who do--you completely know. And it helps you feel less crazy to know that there are others who understand.