(as) sick as a dog
slang Very ill. I haven't been avoiding you, I've just been sick as a dog. I had to go to the doctor on Monday because I was as sick as a dog all weekend.
*sick as a dog
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.
sick as a dog
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.
sick as a dog
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.
sick as a dog
extremely ill. informal(as) sick as a ˈdog
(informal) feeling very ill; vomiting a lot: I was sick as a dog last night.