Nauseated and nauseous are two terms that are both relating to nausea. Moreover, a grammatical difference between them is that nauseated is a verb, while nauseous is an adjective. Nauseated is a term that expresses an action whereby you feel like throwing up or vomiting. On the other hand, nauseous can be said to be the description of the different internal or most likely external factors that makes you feel nauseated.
However, these two terms have their source from the term "nausea," which explains a condition of you wanting to vomit. This is experienced as uneasiness or discomfort in the upper part of your stomach, thus giving you an urge to vomit. This phenomenon is often associated with motion sickness, a discomfort you might experience when you travel. Nevertheless, not all nausea patients really vomit, but most of them do vomit. In addition, nausea is gotten from the Greek word "Nautica", which simply means "motion sickness."