Adrenal Insufficiency (Addison's Disease): This condition is characterized by the inadequate production of cortisol and, in some cases, aldosterone. The lack of aldosterone can lead to hyperkalemia due to decreased potassium excretion. Low morning cortisol levels are a hallmark of adrenal insufficiency, making this the most likely diagnosis given the symptoms.

Congenital Adrenal Hyperplasia (CAH): Certain forms of CAH can lead to deficiencies in cortisol and aldosterone production, similar to Addison's disease, resulting in low cortisol levels and hyperkalemia.
Pituitary Dysfunction: Hypopituitarism can cause a decrease in adrenocorticotropic hormone (ACTH) production, leading to decreased cortisol production. However, hyperkalemia is less commonly associated with this condition unless there's a specific issue with aldosterone production or regulation.

Acute Adrenal Crisis: This is a life-threatening condition that requires immediate attention. It can present with low cortisol levels and electrolyte imbalances, including hyperkalemia. Prompt recognition and treatment are crucial.
Hyporeninemic Hypoaldosteronism: This condition is characterized by a deficiency in aldosterone production, often seen in patients with diabetes or kidney disease, leading to hyperkalemia. While cortisol levels might not be directly affected, the clinical presentation can overlap with adrenal insufficiency.

Familial Glucocorticoid Deficiency: A rare genetic disorder affecting the production of cortisol, which can present with low cortisol levels but is less commonly associated with hyperkalemia.
Pseudohypoaldosteronism Type 1: A rare condition characterized by resistance to aldosterone, leading to hyperkalemia. While it primarily affects infants, some forms can present later in life with variable symptoms, including potentially low cortisol levels in some cases due to associated adrenal dysfunction.