That is the same that happened to me, sorta. I had left my 3ds alone for a little bit to roughhouse with my dog and search this site when the game just froze. The music was still playing, but I can't remember the position my character was in. I was able to turn off my 3ds, but it took a bit longer than it usually did for it to power off (i tried to press the home button and to go into streetpass mode, but neither of those worked)
Thanks for all this information! It's reassuring to know that I'm not alone here. I will be looking to find anyone with a similar issue online! Thanks again. :+)