I have been wondering [but not actively doing research on] how the body responds to traumatic stuff. I'm not sure if it could be considered trauma at all but there was something that heavily bothered me
the brain response of trauma, is it can be act like the things never happened, that’s why some people can decompensate 4 years after a drama, the brain classifies the data by desire for security, with our own will of course, conscientiously or unconsciously we don't want to think about it, so we classify the event as if it had never happened.
And then we decompensate when the brain can no longer classify information, because it requires a lot of energy from the brain when we want to ignore our memories and emotions. This is also the reason why some people develop Stockholm syndrome, kidnapping is so violent for them, to avoid psychic collapse, they will create an emotional bond of attachment with their executioner to better accept and face the situation. Then when they are finally released they collapse some go to suicide unfortunately.
Usagi's situation is a response to an intense trauma, which has illustrated as amnesia. Except that in reality the subject remembers everything that happened very well. Except that he deliberately chooses to forget so as not to face it, but this works him day after day until emotional collapse.
True memory loss, with data deletion, is an organic reaction following a head impact. An emotional shock leads to a sorte of amnesia desired by the victim, except that the memories are not erased or blocked, the persons always remembers it, except that they acts as if nothing had happened, but they are leading a great inner struggle to get to this state. Hence the fact that Mesmer invented hypnosis to free the psyche.
In usagi’s case, « the amnesia » was presented like she was able to lock her brain, like she had a head impact and forget everything. In real life, this is impossible.