Pituitary Apoplexy or Pituitary Tumor: This condition can cause headaches, visual disturbances (including blurred vision), and hormonal imbalances leading to hyponatremia. The pituitary gland's proximity to the optic chiasm can explain the visual symptoms, and its role in regulating various hormones can lead to systemic effects such as hyponatremia.

Hypertensive Encephalopathy: Severe hypertension can lead to encephalopathy, characterized by headaches, vision changes, and sometimes seizures. The hyponatremia could be secondary to the syndrome of inappropriate antidiuretic hormone secretion (SIADH), which can be associated with various conditions, including hypertension.
Chronic Meningitis: This condition can cause chronic headaches, visual disturbances due to increased intracranial pressure, and hyponatremia due to SIADH. Hypertension might be secondary to pain or increased intracranial pressure.
Brain Tumor: Similar to pituitary tumors, other brain tumors can cause increased intracranial pressure, leading to headaches, visual disturbances, and hyponatremia through various mechanisms, including SIADH.

Subarachnoid Hemorrhage: Although typically presenting acutely, a missed or small subarachnoid hemorrhage could lead to chronic symptoms, including headaches and visual disturbances. Hyponatremia can occur due to cerebral salt wasting or SIADH. This diagnosis is critical due to its high mortality and need for urgent intervention.
Temporal Arteritis (Giant Cell Arteritis): This condition can cause severe headaches and visual disturbances, including blurred vision. While hyponatremia is less common, systemic inflammation could potentially lead to SIADH. Missing this diagnosis could result in permanent vision loss.
Preeclampsia: In pregnant women, preeclampsia can cause hypertension, headaches, and visual disturbances. Hyponatremia might be less common but could occur due to various factors, including SIADH. This condition is critical to diagnose due to its potential for severe maternal and fetal complications.

Cushing's Syndrome: This endocrine disorder can cause hypertension and potentially hyponatremia due to mineralocorticoid effects. Headaches and visual disturbances could be indirect effects of hypertension or direct effects of a pituitary adenoma causing Cushing's syndrome.
Adrenal Insufficiency (Addison's Disease): Although more commonly associated with hyperkalemia, certain cases of adrenal insufficiency can present with hyponatremia. Headaches and visual disturbances might be less common but could occur due to hypotension or electrolyte imbalances.
Pseudotumor Cerebri (Idiopathic Intracranial Hypertension): This condition can cause increased intracranial pressure, leading to headaches and visual disturbances. Hyponatremia could potentially occur due to SIADH or other mechanisms. It's more common in obese women of childbearing age.