Perhaps the most mind boggling and inane comments we quite often hear about in our industry about waterbeds are the ones that perpetuate the seasick myth. This is pure ignorance.
Wikipedia defines seasickness as; "A form of motion sickness characterized by a feeling of nausea and, in extreme cases, vertigo experienced after spending time on a craft on water".
This is usually caused by visual confusion and inner ear imbalance due to loss of horizon and constant pitch and roll of the sea for a long period of time.
That said, let me go on the record as saying nobody has ever gotten seasick on a waterbed, period. Many people think it's just a funny thing to comment when they lay down on a full motion watermattress for the first time. As a salesman, many times I would chuckle to be polite, ever pretending to have heard it for the first time, but quickly changing the subject to waveless waterbeds as a "solution" for that "problem".
The truth is, we sell more full motion mattress than we do ultra waveless waterbed mattresses, which clearly indicates that many people love the gentle rolling motion of flotation sleep. A free flow mattress will rock for about 10-15 seconds after laying down, then it will remain motionless until it is pushed again. Different degrees of wavelessness are achieved by manufacturing watermattresses with more or less wave inhibitor inside. These are known as fiberfill mattresses. The greater the density and volume of fiber inside the mattress determines how much motion is reduced. An ultra waveless usually has 8-10 layers of nylon fiber throughout the entire inside (zero second stop), while an 80% waveless watermattress will have 3-5 layers occupying about two thirds of the interior (3-5 second stop). That is how wave reduction is achieved.
So let's hope this puts yet another waterbed myth to bed. Seasickness is caused by the sea, not by a waterbed!