I know it's hard to imagine -- but very large waves can cause these sorts of rolls for large ships. If waves aren't breaking, then a much smaller sailboat is a lot more comfortable (albeit, you might be in the "mixmaster" or washing machine a lot longer ;^) )

You'll note on the first website link below the list of injuries.

http://www.nowpublic.com/world/pacific-sun-cruise-ship-heavy-seas-cctv-video-2660926.html

http://www.dailymail.co.uk/news/worldnews/article-1310049/P-O-Pacific-Sun-cruise-ship-passengers-sent-flying-high-seas-storm.html [includes a picture of the Ship]