Try an export to IDML and re-open that idml file. This will thoroughly re-write the file, and sometimes corruptions go away.
Okay, I successfully exported as an idml file.
But when I try to open the file, I get an error: Cannot open the file "xxxx.idml". Adobe InDesign may not support the file format, a plug-in that supports the file format may be missing, or the file may be open in another application.
I'm guessing it must the missing plug-in? But I have no clue really...
More likley it's still file damage. Try rebooting and trash the prefs again. In case you don't know how to do that correctly, see Replace Your Preferences
You might also want to look at Adobe Forums: InDesign CS5.5 Not Responding for instructions on how to generate a crash from your freeze and get the reports.
Thanks Peter. I was able to use the "Divide and Conquer" method to isolate the corrupted text. Have to reformat a bit, but at least I didn't lose the whole document.