
Nausea
Physical Sensation
'Nausea' often describes a physical feeling related to the stomach, not just a general feeling of sickness. 
Anticipating Vomit
Use 'nausea' when you feel like you might throw up, not for a mild stomachache. 
Intensity Matters
'Nausea' can vary from slight to severe. Specify the intensity if it's relevant. 