Under the weather

Meaning/Usage: Feeling sick; not well

Explanation: When a sailor gets sick on a boat, they would go under the deck and away from the weather to get better. This phrase became popular to express sickness.

"I'm going to stay home because I'm feeling under the weather today."
"I told my boss that I was under the weather. She told me to stay home for the day."
"My wife is feeling under the weather, so I need to get home early today."

A: "Why didn't you come to school today?"
B: "I was under the weather this morning. I need to get some rest."
A: "Well, I hope you start feeling better."

Other Common Sentences:

"I'm feeling a little sick today."
"I don't feel too well."
"I'm not feeling that great. I think I should get some rest."