Brad Schipke explains that trauma happens when an experience overwhelms your conscious mind so completely that it gets pushed into the subconscious. The intense emotions and physical reactions are too much to process, so your mind automatically buries the memory through repression or suppression, leaving it stored below awareness.
Chapters
So what makes a trauma a trauma is that it bypasses your conscious mind here and it goes straight into your subconscious mind because by nature, a trauma overwhelms your conscious mind with all of the emotions and all of the physical reactions that you have from the trauma. Your conscious mind can't comprehend or fully process it in the moment. So what it does in an attempt to protect you is shove it down into your subconscious mind. So since your conscious mind could not process this trauma in the first place, it automatically shoves it down into your subconscious mind and you are forced to hold it there, right? So either from repression where you are pushing it down yourself or suppression where your mind is doing it for you, regardless, either way, it's down in your subconscious mind here, and it's forced underwater.