What version of InDesign are you using?
How many pages is your document?
Is it heavy with images?
Are your images embedded or linked.
Is the option for displaying image quality (display performance) set to high quality?
The number of pages of a document heavily loaded with images can slow down InDesign. You might want to break it up (and use the book feature to link chapters or segments)). Embedded images may also cause the file to be large and may cause lags in document navigation (InDesign 3 files are larger than previous versions), linking them would be better. And lastly, if your display performance is set to high quality, it will surely slow down you file navigation (etc.) make sure it is set to typical or optimized.
Hope that helps.