What causes seasickness?

Seasickness is a result of a conflict in the inner ear, where the human balance mechanism resides, and is caused by a vessel’s erratic motion on the water. Inside the cabin of a rocking boat, for example, the inner ear detects changes in both up-and-down and side-to-side acceleration as one’s body bobs along with the boat. But, since the cabin moves with the passenger, one’s eyes register a relatively stable scene. Agitated by this perceptual incongruity, the brain responds with a cascade of stress-related hormones that can ultimately lead to nausea, vomiting, and vertigo.

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