Viral Gastroenteritis: This is often the most common cause of acute nausea, typically accompanied by vomiting and diarrhea, and is usually self-limiting.

Food Poisoning: Similar to viral gastroenteritis, food poisoning can cause nausea, vomiting, and diarrhea, often resolving on its own within a few days.
Pregnancy: Nausea is a common symptom in early pregnancy, often referred to as morning sickness, although it can occur at any time of day.
Medication Side Effect: Many medications can cause nausea as a side effect, including antibiotics, pain relievers, and antidepressants.
Gastroesophageal Reflux Disease (GERD): GERD can cause nausea, especially after eating, due to the reflux of stomach acid into the esophagus.

Appendicitis: Although less common, appendicitis can present with nausea and vomiting, and if missed, can lead to severe complications, including perforation and peritonitis.
Kidney Stones: Nausea and vomiting can accompany the severe pain of kidney stones, and timely diagnosis is crucial for appropriate management.
Diabetic Ketoacidosis: In patients with diabetes, nausea and vomiting can be symptoms of diabetic ketoacidosis, a life-threatening condition requiring immediate medical attention.
Myocardial Infarction: In some cases, especially in women, nausea and vomiting can be symptoms of a heart attack, making prompt recognition critical.

Brain Tumors: Rarely, nausea can be a symptom of a brain tumor, particularly if it affects areas involved in vomiting centers or increases intracranial pressure.
Addison's Disease: This rare endocrine disorder can cause nausea among other symptoms like fatigue, weight loss, and changes in skin pigmentation.
Porphyrias: A group of rare genetic disorders that can cause acute intermittent porphyria, leading to severe nausea, vomiting, and abdominal pain.
Cyclic Vomiting Syndrome: A rare condition characterized by recurrent episodes of severe nausea and vomiting, often without an identifiable cause.