Amnesia
It had seemed so peaceful, floating in space and waiting for the moment when his oxygen supply ran out. A much calmer and gentler death than he had expected or felt he deserved, but then wasn't that how life often was? The balance between what you got and what was owed to you was so skewed that it seemed impossible to ever bring it back to zero.
Instead of just drifting off into an eternal sleep though. He was found, rescued and brought back into the warmth and relative safety of the human world. Too bad his mind had already decided to take flight and go where it would no longer have to deal with the pain and the death that he had seen; or caused.
It was strange, not knowing who he was where he was from, but in a way it felt familiar too. His world, his life and his memories were a blank white wall and he had no tools with which to decorate them.