This condition is caused by the rocking motion of the craft. Most people tend to concentrate on the inner surroundings,[clarification needed] or close the eyes and try to sleep. This will cause the worst effect of the disturbance.
The brain receives conflicting signals: while the eyes show a world that is still, our body, and in particular the equilibrium sensors located in our ears, send signals of a moving environment. This discordance causes the mind to send to the whole body a general alarm signal, in order to stop all activities,[clarification needed] in particular the most complex of all, the digestion process.
Generally, the disturbance will cease once the visual and motion stimuli are synchronized. This can be obtained concentrating on the horizon until this appears fixed and horizontal. This is the signal that our vision has switched from the reference system of the boat to the reference system of the earth.
The same syndrome: interruption of digestive process, nausea, headache, vertigo, may happen in other conditions and may bear the same name, erroneously. In scuba diving, while happening deep in the sea, so called seasickness is not caused by motion sickness,[dubious– discuss] but by unusual pressure, temperature, stance and medium. Equal syndrome may be experienced hiking at high altitudes.
Over-the-counter medications such as Cinnarizine/Stugeron and prescription medications such as dimenhydrinate,scopolamine and promethazine (as transdermal patches and tablets) are readily available. As these medications often have side effects, anyone involved in high-risk activities while at sea (such as SCUBA divers) must evaluate the risks versus the benefits. Promethazine is especially known to cause drowsiness, which is often counteracted by ephedrine in a combination known as "the Coast Guard cocktail."