Several months on a flight to ORD we were circling out over Lake Michigan (which seems to happen quite a bit) the ride was a little bumpy and then the aircraft suddenly tilted to the right pretty hard - it only lasted a few seconds, and the FA got on the mic and issued a similiar warning regarding a water landing. I felt the same way as you did, staring down at those white caps and wondering to myself just how far I could swim in that freezing water (as if I would be so lucky...)