Nausea is a stomach condition in which the individual feels like they need to vomit. Sometimes this is associated with motion sickness, pressure changes or excessive g-forces.
Lieutenant Malcolm Reed experienced nausea during the shuttlepod 1 mission to Mars in 2155. Doctor Phlox gave him an organic waste bag which he used. (ENT: "Terra Prime")
When asked by Hikaru Sulu what he thought of how they were changing course so much, Ensign Pavel Chekov replied, "I think I'm getting space sick." (TOS: "Amok Time")
After Spock was shot by a poison flower and being injected with medicine, Kirk] asked, "Spock, are you all right?" to which Spock replied, "Dr. McCoy's potion is acting like all his potions, turning my stomach. Other then that, I am quite well." Then McCoy said to Spock, "If your blood were red instead of green, you wouldn't have an upset stomach." (TOS: "The Apple")
Fluctuations in Gravity were known to cause nausea in humanoids. (DS9: "Treachery, Faith and the Great River")
Ezri Dax was known to suffer from space sickness, a condition which can cause nausea, after being joined with the Dax symbiont. (DS9: "Image in the Sand")