If a ship was in a bad weather and its sailors were sick, the crew would go below deck, to get out from "under the weather" to try to feel better.

如果一艘船遇到了坏天气、又恰巧船上的水手生病了，船员会到甲板下面，避免直接“在天气下面”(under the weather)。让自己感觉好点。

youdao

Other passengers reported no air-conditioning inside cabins and an increasing stink inside the ship from sick passengers and a lack of food refrigeration.

BBC: Carnival Triumph: Conditions 'worsen' on stranded ship