Looks like it could be a memory leak in DW. Were you working on the page for a while before it happened? What version of CSS Sculptor? What version of DW? What OS?
Our solution for this issue, since it appears to be a native DW issue has been to add an autosave feature so that if the application crashes unexpectedly you can pick up where you left off. We've added this in recent products and builds with large interfaces where users might make a lot of changes and this problem can result.
I don't recall if we have added the autosave feature to CSS Sculptor yet, but if you give me more feedback I can look into it more and possibly get you a build with autosave. It wouldn't prevent the problem from occurring, but it would make it so that you wouldn't have to start over when it did.