Which electrolyte abnormality is most likely indicated by headache, nausea, vomiting, and confusion without bony pain?

The symptoms presented—headache, nausea, vomiting, and confusion—are commonly associated with an electrolyte imbalance known as hyponatremia, which is a low sodium level in the blood. Sodium plays a critical role in maintaining fluid balance and proper function of muscles and nerves. When sodium levels drop, it can lead to cellular swelling, particularly affecting the brain, which can result in neurological symptoms such as headache and confusion.

Nausea and vomiting can also occur as the body responds to the changes in sodium levels. The absence of bony pain further supports hyponatremia, as conditions like hypercalcemia would typically present with additional symptoms such as bone pain or abdominal issues due to increased calcium levels. Hyponatremia is, therefore, the most likely electrolyte abnormality indicated by the given symptoms.

While hyperkalemia can also cause some neurological symptoms, it more often presents with muscle weakness or palpitations rather than the specific combination of symptoms listed in this question. Hypomagnesemia may lead to muscle cramps and neurological issues, but it does not primarily cause the confusion or gastrointestinal symptoms described. Hence, hyponatremia aligns most closely with the clinical picture presented.