All pictures now in collage format

[NanOcon]

The other day, out of nowhere, I opened my gallery and ALL of my pictures are now in collage format, instead of the small rectangular views/thumbnails they've always been in. All 1200 or so pics. So now I have some pics taking up the entire width of the screen, some are tiny, all different sizes and shapes. You can't even manually pick more than 6 pictures to put in a collage, so I couldn't have done this by accident. I have checked every setting, and looked for updates. I see nothing different or changed. Has this happened to anyone else? Am I missing something really obvious? WTH? It's annoying as hell. Thanks for any input on this one.