I opened Garry's Mod earlier, and noticed that all of my addons (installed from the Steam Workshop) were missing. Not disabled, but missing: it says "None Found!" when I open the addons menu. The files seem to still be on my hard drive, and the workshop shows I'm still subscribed to them;, and they load fine in offline mode. What's going on?
Update: Aaaaaand it's working now. I think it may have been a problem with Steam/the Workshop--the in-game browser wasn't working properly before. I guess it's been fixed now.
Update 2: See my answer below.