Pre-nausea pathophysiology
It has been described that alterations in heart rate can occur as well as the release of vasopressin from the posterior pituitary. Diagnosis
Patient history
Taking a thorough patient history may reveal important clues to the cause of nausea and vomiting. If the patients symptoms have an acute onset, then drugs, toxins, and infections are likely. In contrast, a long-standing history of nausea will point towards a chronic illness as the culprit. The timing of nausea and vomiting after eating food is an important factor to pay attention to. Symptoms that occur within an hour of eating may indicate an obstruction proximal to the small intestine, such as gastroparesis or pyloric stenosis. An obstruction further down in the intestine or colon will cause delayed vomiting. An infectious cause of nausea and vomiting such as gastroenteritis may present several hours to days after the food was ingested. The contents of the emesis is a valuable clue towards determining the cause. Bits of fecal matter in the emesis indicate obstruction in the distal intestine or the colon. Emesis that is of a bilious nature (greenish in color) localizes the obstruction to a point past the stomach. Emesis of undigested food points to an obstruction prior to the gastric outlet, such as achalasia or Zenkers diverticulum. If patient experiences reduced abdominal pain after vomiting, then obstruction is a likely etiology. However, vomiting does not relieve the pain brought on by pancreatitis or cholecystitis.
Psychiatric
Nausea may be caused by depression, anxiety disorders and eating disorders. Potentially serious
While most causes of nausea are not serious, some serious conditions are associated with nausea. These include pancreatitis, small bowel obstruction, appendicitis, cholecystitis, hepatitis, Addisonian crisis, diabetic ketoacidosis, increased intracranial pressure, spontaneous intracranial hypotension, brain tumors, meningitis, heart attack, rabies carbon monoxide poisoning  and many others. Comprehensive list
Inside the abdomen
Obstructing disorders

Gastric outlet obstruction
Small bowel obstruction
Colonic obstruction
Superior mesenteric artery syndromeEnteric infections

Viral infection
Bacterial infectionInflammatory diseases

Celiac disease
Cholecystitis
Pancreatitis
Appendicitis
HepatitisSensorimotor dysfunction

Gastroparesis
Intestinal pseudo-obstruction
Gastroesophageal reflux disease
Irritable bowel syndrome
Cyclic vomiting syndromeOther

Non-celiac gluten sensitivity
Biliary colic
Kidney stone
Cirrhosis
Abdominal irradiation

Outside the abdomen
Cardiopulmonary

Cardiomyopathy
Myocardial infarction (heart attack)
Paroxysmal coughInner-ear diseases

Motion sickness
Labyrinthitis
MalignancyIntracerebral disorders

Malignancy
Hemorrhage
Abscess
Hydrocephalus
Meningitis
Encephalitis
RabiesPsychiatric illnesses

Anorexia and bulimia nervosa
DepressionOther

Post-operative vomiting
Nociception

Medications and metabolic disorders
Drugs

Chemotherapy
Antibiotics
Antiarrhythmics
Digoxin
Oral hypoglycemic medications
Oral contraceptivesEndocrine/metabolic disease

Pregnancy
Uremia
Ketoacidosis
Thyroid and parathyroid disease
Adrenal insufficiencyToxins

Liver failure
Alcohol

Pathophysiology
Research on nausea and vomiting has relied on using animal models to mimic the anatomy and neuropharmacologic features of the human body. The physiologic mechanism of nausea is a complex process that has yet to be fully elucidated. There are four general pathways that are activated by specific triggers in the human body that go on to create the sensation of nausea and vomiting. Central nervous system (CNS): Stimuli can affect areas of the CNS including the cerebral cortex and the limbic system. These areas are activated by elevated intracranial pressure, irritation of the meninges (i.e. blood or infection), and extreme emotional triggers such as anxiety. The supratentorial region is also responsible for the sensation of nausea. Chemoreceptor trigger zone (CTZ): The CTZ is located in the area postrema in the floor of the fourth ventricle within the brain.