Collections have vanished from Bridge - help???

Working off an external drive, and I've just gone to edit from my Collections, but not a single one is showing! They've all completely gone! Freaking out as the process of going through 40 odd games (sports photographer) to create new client Collections (for editing) is going to take soooo long.  Any idea what has happened as is there any way to get them back??  They were there last night.  But they are not there now. 😞