Under the weather

Feeling unwell, physically or emotionally out of sorts, often due to sickness, fatigue, or a general malaise. It's broad enough to cover minor ailments.

This nautical phrase hails from the 19th-century maritime world, where sailors who were feeling ill were sent below deck, away from the harsh weather conditions topside-literally 'under' the wind, rain, or waves. Ships' logs from the era note crew being 'under the weather' during storms. It appeared in print by 1827 in American seafaring tales, and as sailing culture influenced English slang, it transitioned to land-based use, retaining its vivid imagery of nature's impact on human frailty.