sick as a dog, to be

Cliché very sick; sick and vomiting. (*Also: as ~.) We've never been so ill. The whole family was sick as dogs. Sally was as sick as a dog and couldn't go to the party.

Very ill, especially from a stomach malady. For example, I don't know what was in that stew but I was sick as a dog all night. This simile was first recorded in 1705. Why a dog should be viewed as particularly sick remains unclear.

If you are as sick as a dog, you are very ill. The last time I ate shellfish I was sick as a dog for 48 hours afterwards.

To feel very ill, particularly to feel nauseated. Despite being touted as man’s best friend, dogs are often maligned. This proverbial simile dates from the sixteenth century or earlier and is still current. Occasionally it has appeared with sick meaning “tired of,” as by David Garrick (Neck or Nothing, 1766, 1:1): “I am sick as a dog of being a valet.”