Aspiration Pneumonia: This is the most likely diagnosis because vomiting can lead to aspiration of gastric contents into the lungs, causing a chemical pneumonitis that can significantly decrease oxygen saturations.

Pulmonary Embolism: Although less common, vomiting can be a symptom of a pulmonary embolism, especially if the patient has been immobile or has other risk factors. The sudden drop in saturations could be due to a blockage in a pulmonary artery.
Gastrointestinal Bleed: Vomiting blood (hematemesis) can lead to hypovolemia and decreased oxygen delivery to tissues, potentially causing a drop in oxygen saturations.
Dehydration and Electrolyte Imbalance: Severe vomiting can lead to dehydration and electrolyte imbalances, which can affect cardiac function and lead to a decrease in oxygen saturations.

Cardiac Tamponade: Although rare, cardiac tamponade can present with vomiting and a drop in oxygen saturations due to decreased cardiac output. It's crucial to consider this diagnosis because it requires immediate intervention.
Pneumothorax: A spontaneous pneumothorax can cause sudden chest pain, vomiting, and a drop in oxygen saturations. It's a life-threatening condition that needs prompt diagnosis and treatment.
Anaphylaxis: Anaphylactic reactions can cause vomiting, respiratory distress, and a drop in oxygen saturations. Given its potential for rapid progression to a life-threatening state, it must be considered.

Foreign Body Aspiration: While more common in children, adults can also aspirate foreign bodies, which can cause a sudden drop in oxygen saturations if the object obstructs an airway.
Eclampsia: In pregnant women, severe vomiting can be a symptom of eclampsia, a condition characterized by seizures in pregnant women with pre-eclampsia. It's rare but critical to diagnose due to its severe implications for both mother and fetus.