This has happened two or three times over the past few days. I think the 3DS just thinks it went asleep. This has happened while playing pokemon platinum and when it happened it one time the 3DS was near a laptop and the other time it was near a ds lite. I'm not sure if that has anything to do with it. This issue quickly goes away when it happens but I'm afraid something might be wrong with the 3DS. Platinum is on an official cartridge I bought new about a decade ago, also the 3DS has not been modded what so ever.