I came across this above youtube video from Jalopnik.com given here
If I was on board, I'd probably jump off as soon as I could, because That Does Not Look Right.
But everything is all right, according to the video, and big ships are designed to twist about in heavy seas, much like airplane wings bend in turbulence. If they weren't flexible, they would break.
That doesn't make it feel any better though. I'd be putting on my lifejacket.