Gastroesophageal Reflux Disease (GERD): This condition can cause sudden vomiting, especially after eating, due to the reflux of stomach contents into the esophagus. The absence of preceding nausea does not rule out GERD, as the vomiting can be a direct result of the reflux.

Food Poisoning: Sudden vomiting can be a symptom of food poisoning, which may not always be preceded by nausea. The onset of symptoms can be rapid, depending on the type of contaminant.
Viral Gastroenteritis: Although often accompanied by nausea, viral gastroenteritis can cause sudden vomiting as a primary symptom, especially in children.
Migraine: Some individuals with migraines may experience vomiting without prior nausea, especially if the migraine is primarily abdominal or if the individual has a history of cyclic vomiting syndrome.

Appendicitis: Although classically presenting with abdominal pain, nausea, and vomiting, appendicitis can occasionally present atypically, with sudden vomiting being an initial symptom, especially if the appendix is located in an unusual position.
Intestinal Obstruction: This is a surgical emergency that can present with sudden vomiting, which may not be preceded by nausea. The vomiting can be bilious or non-bilious, depending on the level of obstruction.
Increased Intracranial Pressure: Sudden vomiting without nausea can be a sign of increased intracranial pressure, which could be due to various causes such as a brain tumor, hemorrhage, or other space-occupying lesions.

Cyclic Vomiting Syndrome: A rare condition characterized by recurrent episodes of severe vomiting lasting hours to days, with periods of normal health in between. It can start suddenly without preceding nausea.
Ruptured Ovarian Cyst: In females, a ruptured ovarian cyst can cause sudden, severe vomiting, among other symptoms like abdominal pain, without prior nausea.
Porphyria: A group of rare disorders that can cause acute episodes of severe vomiting, abdominal pain, and neurological symptoms, which may not always be preceded by nausea.