InDesign not responding

16GB of RAM is the bare minimum but it shouldn't cause InDesign to freeze. As the others have noted, we really need to know more about the file sizes. Additional info would be the operating system and processor.

Before you do anything else trash your preferences and see if that helps.

123 Gb, really? Don't forget to do indd -> imdl -> indd as Robert says.

Are you embed images inside InDesign file instead of linking (CTRL+D)? 

How ofter have you done SAVE AS with new name on your INDD file?

Or were you only doing SAVE?

If you are still able to open your INDD file - save it with a new name.

InDesign is always keeping Undo history - unfortunately, it's available ONLY till you close your document - but still kept in your INDD file after you save - so you have to do SAVE AS with a new name from time to time - the frequency depends on the number of changes you've made - but at least daily would be good and you'll have backup copy as a bonus. 

Also, you can do IDMLing - Export your file as IDML - then open it and save with a new name - so you won't overwrite your original file.