Gastroenteritis: This is often the first consideration for patients presenting with vomiting, especially if it's watery. The absence of fever, abdominal pain, or diarrhea might suggest a viral cause, which is common and usually self-limiting.

Food Poisoning: Similar to gastroenteritis, food poisoning can cause vomiting without the other symptoms mentioned, depending on the causative agent.
Viral Gastroenteritis (Norovirus): A common cause of outbreaks of vomiting, often without fever or diarrhea, especially in closed environments.
Pregnancy-related Morning Sickness: Although typically associated with early pregnancy, it could be considered if the patient is female and of childbearing age, even if she doesn't suspect pregnancy.
Medication-induced Nausea and Vomiting: Certain medications can cause nausea and vomiting as side effects, which could fit this presentation if the patient has recently started a new medication.

Appendicitis: Although the patient denies abdominal pain, appendicitis can sometimes present atypically, especially in early stages or in certain populations like the elderly or young children. Missing this diagnosis could lead to severe consequences.
Intestinal Obstruction: This is a surgical emergency that can present with vomiting. Early on, the vomiting might be the only symptom, and it's crucial not to miss this diagnosis.
Pancreatitis: While typically associated with abdominal pain, some cases of pancreatitis can present with nausea and vomiting as primary symptoms, especially if the pain is not severe or is atypical.
Increased Intracranial Pressure: Rarely, increased intracranial pressure can cause vomiting without headache, especially if the patient is unable to communicate effectively or if the condition develops slowly.

Cyclic Vomiting Syndrome: A condition characterized by recurrent episodes of severe vomiting lasting hours to days, with periods of normal health in between. It's rare and often diagnosed after other causes have been ruled out.
Gastroparesis: A condition where the stomach takes too long to empty its contents, which can cause nausea, vomiting, and feeling full after eating only a small amount of food. It's less common and might be considered if other diagnoses are excluded.
Rapid Gastric Emptying (Dumping Syndrome): Typically occurs after gastric surgery and can cause vomiting among other symptoms, due to food, especially sugar, moving too quickly from the stomach to the small bowel.