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.
Related Words for sick as a dog restless, sickly, groggy, anxious, squeamish, uncomfortable, uneasy, fidgety, diseased, ill, weak, feeble, woozy, infirm, ailing, afflicted, poorly, disordered, indisposed, down