Nausea is the feeling of discomfort that occurs prior to vomiting. There are many possible causes for nausea, such as hormonal fluctuations, allergic reactions and motion sickness, and it may be intermittent or chronic in nature.
Morning sickness---a type of nausea that occurs upon waking---is a common occurrence in pregnant women. Recurrent bouts of morning nausea may indicate pregnancy in women of child-bearing age.
Allergies are capable of causing nausea and vomiting. According to mayoclinic.com, nausea is among the most common symptoms of food allergy.
Gastroparesis is the inability of the stomach to empty its contents in the absence of a blockage. It can cause nausea and vomiting and is often associated with diabetes, according to nih.gov.
An ulcer is a sore in the stomach or duodenum (small intestine). Recurrent nausea and vomiting--especially when occurring after eating large meals--may be a sign of an ulcer.
While usually not dangerous, recurrent nausea can sometimes signal a more serious problem. If you experience recurrent nausea, vomiting or other intestinal symptoms, talk to your doctor about your treatment options.