Nausea and dizziness caused by the rocking motion of a boat or ship at sea.
Compound of 'sea' (from Old English 'sæ') and 'sickness' (from Old English 'seocnes'). The condition was named once maritime travel became common enough to be a widespread problem.
Seasickness happens because your eyes tell your brain you're still while your inner ear detects motion—your brain literally can't decide which sense to trust, so it creates confusion that makes you nauseous as a form of protection.
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