Why is Amnesia the beginning of every rpg and a ton of movies. Amnesia has nothing to do with losing your previous memories, it only affects your ability to store short term memories, basically you can't remember what happened ten minutes ago, but everything before the brain damage is fine, also you don't recover, ever. So for all that is holy, do not start your game out with "You woke up with Amnesia and cannot remember your past." If you feel it neccessary, blame it on a monster that steals memories.
Thanks you and have a nice day.