The idiom "under the weather" means feeling sick, especially sick with the flu or a common cold. These examples will help you understand this idiom.
Idiom Land — Idiom of the day: Under the weather. Meaning: To
Weather Idioms Callan School Barcelona
Idiom – Under the weather
The Most Common English Idioms - Word Coach
7 Everyday English Idioms and Where They Come From
English idiom: under the weather
33 weather idioms and idiomatic expressions
Idiom – under the weather - Online English Lab
Under the Weather – Idiom, Meaning and Origin
Idiom: Under the weather (meaning & examples)
American English Idiom - Under the Weather
Weather On The Go: Rain idioms and phrases - ABC Education
Health idioms and expressions - Mingle-ish
Idiom Examples: Common Expressions and Their Meanings