Adrenal Insufficiency: This condition, particularly primary adrenal insufficiency (Addison's disease), can lead to hyperkalemia due to the lack of aldosterone, hyponatremia due to the lack of aldosterone and cortisol, and hypoglycemia due to the lack of cortisol. The combination of these electrolyte imbalances and metabolic disturbances makes adrenal insufficiency a strong candidate for the single most likely diagnosis.

Renal Failure: Acute or chronic renal failure can cause hyperkalemia due to the kidney's inability to excrete potassium, hyponatremia due to water retention and inability to concentrate urine, and hypoglycemia in advanced stages due to impaired gluconeogenesis and glucose release. The severity and combination of these symptoms can vary depending on the stage and type of renal failure.
Hepatic Failure: Liver failure can lead to hypoglycemia due to impaired gluconeogenesis and glycogenolysis, hyponatremia due to water retention and secondary hyperaldosteronism, and hyperkalemia in certain cases due to the release of potassium from liver cells or secondary renal effects.

Pituitary Apoplexy: Although rare, pituitary apoplexy can lead to acute adrenal insufficiency (due to ACTH deficiency), causing the aforementioned electrolyte and metabolic disturbances. It's crucial not to miss this diagnosis due to its potential for severe and rapid deterioration.
Type 1 Diabetes Mellitus with Renal Complications: In the context of diabetic ketoacidosis (DKA) or hyperosmolar hyperglycemic state (HHS), there can be significant electrolyte imbalances. However, the presence of hypoglycemia instead of hyperglycemia might indicate a different stage or complication of the disease, such as renal failure affecting potassium and sodium levels.

Familial Hyperkalemic Periodic Paralysis: A rare genetic disorder that affects potassium channels, leading to episodes of hyperkalemia, which could theoretically be associated with other electrolyte imbalances and metabolic disturbances in certain contexts.
Congenital Adrenal Hyperplasia (CAH): Certain forms of CAH can lead to deficiencies in aldosterone and cortisol, similar to adrenal insufficiency, resulting in hyperkalemia, hyponatremia, and potentially hypoglycemia, especially in undiagnosed or untreated cases.
Insulinoma: A rare tumor of the pancreas that produces excess insulin, leading to hypoglycemia. While it primarily causes hypoglycemia, in rare cases, it could be associated with other electrolyte disturbances, especially if there are secondary effects on kidney function or if the patient has co-existing conditions.