This has both a Literal and figurative meaning. Literally it means "about to vomit" and figuratively, it signifies the feeling caused by utter disgust. See these links to see more examples : http://dictionary.cambridge.org/dictionary/british/sick-to-your-stomach http://www.idiomquest.com/learn/idiom/sick-to-my-stomach/ http://idioms.thefreedictionary.com/feel+sick+to+stomach

The phrase refers to anything that is so repulsive it would cause you to vomit; however, it has now become an English idiom meaning "that is disgusting".