Typical indicators of sea sickness are a dry mouth, cold sweat, dizziness and nausea, sometimes followed by vomiting.

Medically speaking, sea sickness is a variation of motion sickness or kinetosis. Although it does not always end up with the affected person "feeding the fishes", it can ruin a boat trip but, with the right medicine and a few useful tips, it can be kept under control.

Kinetosis is caused when "the body experiences difficulty with different and contradictory stimuli", according to Michael Knappich, a doctor at the Berlin Center for Travel and Tropical Medicine.

The rocking motion experienced at sea causes a discrepancy between what the eye can see and what our body's sensory organs are telling our brains.

In the process, the body produces more histamines. According to a new theory by Reinhard Jarisch, an allergist from Vienna, histamines are the cause of the symptoms of sea sickness.

Almost everyone can be affected by sea sickness. But the degree to which individuals feel sick can vary greatly. "There are people who are very susceptible and those who don't have any problems at all," says Knappich.

People also react differently to the degree to which a boat rocks. "Some people feel very sick with just a small movement, while only a long, rolling movement will cause sea sickness in others," says Andreas Koch, a doctor at the German navy's medical institute in Kronshagen near Kiel.

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