Seasickness is related to the whole question of equilibrium and dizziness. Our organs of balance contain certain stiff hairs which are surrounded by liquid. When we move in any direction, the liquid moves the hairs. These hairs send a message to the brain, which gives us the sensation of moving in that direction.

In our normal activities this liquid, called lymph, are such that our bodies can adjust to changes easily and we manage to keep our balance. But what happens on a ship? As the position of the deck changes under our feet, the lymph is shaken back and forth. It actually rocks to and fro, and from side to side.