According to WebMD, nausea is an uneasy feeling in the stomach that a person typically experiences before vomiting. Nausea and vomiting are not diseases in themselves but are symptomatic of a number of medical conditions.
WebMD explains that vomiting following nausea occurs in various psychological illnesses and emotional states, including bulimia, intense pain and emotional stress. Food poisoning and motion sickness are other common causes of nausea and vomiting. In food poisoning, nausea and vomiting typically occur within one to eight hours of ingesting tainted food, but some bacteria, such as salmonella, can take longer to produce symptoms. Nausea and vomiting sometimes indicate serious medical conditions, such as heart attack, brain injury, brain tumors and some other forms of cancer