DS Game Trouble

Well, I just recently finished the third temple in Phantom Hourglass, and I was aboard the Ghost Ship. I saved, and left the DS in a secure place for a few days. When I came back to play it, both files were missing. I'm pretty sure that nobody touched the DS; it was in the same position in a hidden place. Anyway, what may be the problem with my game?

I've had this happen (although not with my DS) Sometimes if a cartridge is hit or jarred the memory can be deleted or corrupted. Possibly the same happened with PH.