a bunch of my albums just disappeared?

Are you using iPhoto or Photos for Mac? I am asking, because this article is showing as related above your question: If you're missing photos or videos in the Photos app

If you are using Photos for Mac, you may want to check, if only the albums are missing and your photos are still in "All Photos". Albums can temporarily vanish, if you just enabled iCloud Photos on one of your devices. The iCloud sync of several devices may need to merge the photos and albums between devices and while the merging is solving conflicts between albums from several devices, they may be temporarily hidden.

Restore from your back up is the obvious solution.