Gastroenteritis: This is often the most common cause of nausea and vomiting, typically resulting from a viral or bacterial infection. It's characterized by inflammation of the stomach and intestines, leading to symptoms like diarrhea, abdominal cramps, and fever, in addition to nausea and vomiting.

Food Poisoning: Similar to gastroenteritis, food poisoning can cause nausea and vomiting, usually after consuming contaminated or spoiled food. Symptoms can vary depending on the causative agent but often include abdominal cramps and diarrhea.
Pregnancy: Morning sickness is a common symptom experienced by many women during early pregnancy, characterized by nausea and vomiting, often triggered by certain smells or tastes.
Motion Sickness: This condition occurs in response to certain motions, such as during travel by car, boat, plane, or other vehicle, leading to nausea and vomiting.
Medication Side Effects: Many medications can cause nausea and vomiting as side effects, including antibiotics, pain relievers, and chemotherapy drugs.

Appendicitis: Although less common, appendicitis can present with nausea and vomiting, especially if the appendix ruptures. It's crucial to consider this diagnosis to avoid missing a potentially life-threatening condition.
Kidney Stones: Severe pain, nausea, and vomiting can be symptoms of kidney stones, particularly if they cause an obstruction.
Pancreatitis: Inflammation of the pancreas can lead to severe abdominal pain, nausea, and vomiting, requiring immediate medical attention.
Intestinal Obstruction: This condition, where part of the intestine is blocked, can cause severe nausea and vomiting, among other symptoms, and is a medical emergency.

Brain Tumors: In rare cases, nausea and vomiting can be symptoms of a brain tumor, especially if it's located in an area that affects balance and coordination, such as the cerebellum.
Meningitis: Although primarily known for causing fever, headache, and stiff neck, meningitis can also lead to nausea and vomiting in some cases.
Gastroparesis: A condition where the stomach takes too long to empty its contents, gastroparesis can cause nausea, vomiting, and feeling full after eating only a small amount of food.
Cyclic Vomiting Syndrome: A rare disorder characterized by recurring episodes of severe nausea and vomiting, often without an identifiable cause.