Force quit and restart ID. If you're lucky, yoru file will reopen and you'll not have lost more than a few minutes work. Resave with a NEW name so you don't overwrite the old file (you're going to want to keep that for backup, just in case).
If that doesn't work, close ID and find the InDesign Revovery folder (it's hidden on most OS versions now) and empty it, then restart ID. You should be able to open the last-saved version of your file. InDesign Recovery is normally in the same path as the InDesign SavedData file. You find that listed in Replace Your Preferences
I'll try this. hope it works!