I know that it doesn't happen on too many occasions, fortunately, but every now and then rough seas cannot be avoided. In 24 cruises, this has only happened three times and having a low, midship cabin has always helped. However, it can also add to the experience of rough seas.
Check out this 10 second clip from the Brilliance of the Seas. We were in a Deck 2 porthole cabin and could figure out what we were hearing until we opened the curtain and looked at what was happening against our window/porthole.