What is a common symptom of excessive antidiuretic hormone levels?

Excessive levels of antidiuretic hormone (ADH), also known as vasopressin, can lead to a condition known as Syndrome of Inappropriate Antidiuretic Hormone secretion (SIADH). In this scenario, one of the primary effects is the retention of water by the kidneys, which dilutes the sodium levels in the blood. As a result, hyponatremia, or low sodium concentration, occurs. This condition is characterized by a variety of symptoms, including confusion, seizures, and muscle cramps, which stem from the disrupted balance of fluids and electrolytes in the body.

In contrast, increased thirst is more typically associated with dehydration or conditions like diabetes insipidus, where there is a deficiency of ADH. Frequent urination occurs with conditions that lead to high urine output, which is contrary to the water retention seen in excessive ADH levels. Lastly, high blood sugar is related to glucose regulation rather than fluid balance and sodium concentration, and is not a symptom of elevated ADH levels. Therefore, hyponatremia is indeed the most relevant symptom associated with excessive antidiuretic hormone levels.