Have never heard of this problem, so have no clue. You must have hit some odd key. Seems unlikely Bridge would delete your actions.
If what you see in the Actions Palette is Adobe Photoshop action that get installed by default it sound like your Photoshop Preferences Folder was wiped out and recreated by Photoshop. If your Actions Palette is empty it sounds like the file "Actions Palette.psp" been hosed in your Preferences folder. You should be able to recover your action from your backup if you did not save your actions to disk.