Wiktionary
sick as a dog
a. (context simile English) Very ill.
Usage examples of "sick as a dog".
Peter Meinert-Neilsen's knee was sore, Kevin was sick as a dog from the temperature changes in the Alps, and Frankie and George were blown from carrying the load.
Panting, Frazer dragged the sari and blankets from his head, feeling as sick as a dog.
Pa had come back, he was drinking some more, and he ate a lot of it -- almost the whole thing, and it made him sick as a dog, and he went and wasted all of it.
Three hours later I was on hands and knees under the cotton trailer, as sick as a dog.
Once he had the Wealth stone, he would return here and buy out the place and gorge himself sick as a dog!