The human mind is complex and not fully understood. Which, when you think about it, makes it perfect for a plot device.
Who says that you can't suddenly forget or remember something? Who says you can't only remember certain things, like fighting skills, while forgetting the rest of your identity? Who knows if you can suddenly remember an alien abduction after you were sure that you were just sleepwalking at night?
Playing tricks on your characters' memories can be a great way to move your plot forward, but it isn't always realistic (or new). Take a good look at the ways memories are informing your narrative and see if it's the right way to use this well-known trope.