Definitions:
Nauseous – causing nausea
Nauseated – feeling nausea
Many people say they are nauseous when they feel sick. Some will argue that they are saying that they cause nausea. Others say it is acceptable to use nauseous in that manner since it is so widely used that way.
So, which do you use when you are feeling sick? I suggest that you research the two words and then decide for yourself which you prefer.