Nausea is the sensation of unease and discomfort from the stomach, with the sufferer feeling that he is about to vomit (though he may not actually do so).
It is a symptom of a huge variety of conditions, from motion sickness to morning sickness and encompassing viral infections and many other diseases. It is a side effect of many drugs, both therapeutic and recreational.
Whilst short-term nausea and vomiting are in themselves harmless, they are indicative of some disease which may be serious, and a longer episode can result in serious dehydration, which is dangerous.
Symptomatic treatment for nausea and vomiting usually includes avoidance of solid food (which is usually easy as nausea suffers tend not to want to eat) and rehydration (with electrolyte solutions if the symptoms have been persistent).
Nausea (French La Nausée) is a novel by Jean-Paul Sartre.