Nausea

Nausea was a stomach condition in which the individual felt like they needed to vomit. Sometimes this was 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. 

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."

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."

Worf had a very weak stomach when it came to zero gravity, becoming ill while attempting zero-gravity combat training at Starfleet Academy. 

Fluctuations in gravity were known to cause nausea in humanoids. 

Ezri Dax was known to suffer from space sickness, a condition which can cause nausea, after being joined with the Dax symbiont. 

B'Elanna Torres felt nauseous after being infected by a macrovirus Tom Paris was surprised by this since Klingons have a redundant Stomach. )