What is the physiology of sea-sickness?

Can someone explain to me the physiology that is invovled with a person getting sea sick/motion sickness?

Your sense of balance comes from a fluid in your inner ear. The rocking motion of the sea or other movement gives your body a sense of motion that it tries to match with your other senses, typically vision. If the motion does not match what you are seeing, your brain interprets this as something not being right with your body and triggers a response. Something like "well, we arent moving so maybe we ate something that is poison, lets get rid if it" and then you hurl.

Seasickness is 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. It is typically brought on by the rocking motion of the craft. Some people who are particularly vulnerable to the condition can feel seasick simply by setting foot on a boat, even if the vessel is in dry dock.[citation needed]Others are relatively immune, or become immune through exposure.

Seasickness can be a debilitating condition and can be dangerous if the sufferer has an important role to carry out, such as steering a yacht through stormy seas while avoiding rocks and other hazards. It is also particularly hazardous for scuba divers who, through dehydration following vomiting, are at increased risk of decompression illness.