under the weather

1. Indisposed, unwell: “The day after the big party, Jay had to call in sick, saying he was feeling under the weather.”

Idioms and Phrases

Ailing, ill; also, suffering from a hangover. For example, She said she was under the weather and couldn't make it to the meeting . This expression presumably alludes to the influence of the weather on one's health. [Early 1800s] The same term is sometimes used as a euphemism for being drunk, as in After four drinks, Ellen was a bit under the weather .