Hi PeppersGhost
I love that name, your books sound really good, i will try to help you as much as i can.
memory is not my are of expertise so i can only share what i have expereienced through my work with people and what bits of knowledge i have picked up through my personal interest in psychology.
The most serious and prominent causes of memory loss as far as i am aware come form organic and aquired brain damage. some form of dementia for example or an accident/disease that damages certain areas of the brain. this is probably not the type of memory loss that you would be interested in for your story. however the syptoms of these types of problems are so pronounced that they make a good subject for studying memory loss. i have spent time working on a ward that cares only for patients with demnetia. this really was an illuminating experience to watch people interacting with each other without being able to remember who they are or where they where. working there it dawned on me just how horrific this problem was. i watched as a group of patients walked around the corridors of the ward trying doors and conversing what each door was for, they where evidently trying to help each other find a way out of the ward but they had no idea where they where or how they got there despite having lived on the ward for weeks or months. i imagined it was similar to how i heard of gold fish that go around and around the fish bowl with such a short memory that each time they went around the place was like new.
another form of short term memory loss comes from chronic intense emotional states such as anxiety and depression. a gentleman that i work with is physically very fit and healthy but suffers from chronic anxiety and depression such that he has short term memory loss and confusion. this man has started to believe that he has some form of dementia because of his persistent forgetfulness and confusion. his belief about having dementia feeds back into his anxiety and so makes him even more anxious, confused and forgetful, reinforcing his belief about dementia in a viscious negative cycle of reinforcment.
the type of memory loss that you will be intersted in for your story is known as repression.
this theory of repression comes from the psychoanlytic schools of psychology, again this is not my area of understanding and i am not an advocate of psychoanalytic psychology.
this is where memories are pushed out of conscious experience and the representation to the mind is prevented from occuring due to the unfavourable quality of the memories or thoughts. an example may be somebody that was abused at a young age. who has blcoked out the memory of the act of abuse, the memory is still there but it has been prevented from being experienced by the conscious mind. this repressed memory will effect the conscious mind by causing the individual to react negatively to any experience which could be associated with the initial act.
this theory could be easily adapted to your character, with a little imagination and creativity. no need for a history of abuse or anything unsavoury. any situation that may need to have a memory blocked or prevented from accessing the conscious mind. maybe a lie that he has told or a defeat that he does not want to remember.
hope i have explained this alright, i dont pretend to know what i am talking about with repression but that is how i understand it myself, if any one can give a better explanation i would appreciate that myself.
also there is a lot more to memory than what i have been able to share here so perhaps somebody else may be able to chip in with some better inforamtion for you.