Lost Favorites Album
Apple Photos - What did I do? I was viewing my "Favorites" album and I wanted to remove one photo from Favorites. l simply clicked on the heart icon (because I'm a dummy and don't really know how to work with Albums in Apple Photos). It turned red briefly, then my entire Favorites album went away and I cannot find it. The photos that were in the album also seem to be gone, and they were, after all, my favorites! They do NOT show up in the Recently Deleted collection.
iMac, 10.11