Adrenal Insufficiency / Addison's Disease is destruction of the adrenal cortex causing cortisol and aldosterone deficiency. The clinical picture follows hormone absence: cortisol loss → hypoglycemia, fatigue, inability to mount a stress response; aldosterone loss → sodium wasting + potassium retention → hyponatremia, hyperkalemia, orthostatic hypotension. The pathognomonic finding is hyperpigmentation — bronze skin in sun-exposed areas, pressure points, buccal mucosa, and skin creases — driven by ACTH excess stimulating melanocytes (MSH cross-reactivity). This is specific to PRIMARY adrenal insufficiency. Adrenal (Addisonian) crisis: vascular collapse, profound hypotension, abdominal pain, fever, altered mentation — triggered by physiologic stress (infection, surgery, trauma, missed steroid dose) in an undertreated patient. Priority interventions: IV access, NS infusion, IV hydrocortisone 100 mg bolus, glucose monitoring — do NOT delay steroids waiting for labs. Boards test: immediate hydrocortisone as the life-saving priority; stress-dosing education (double dose during moderate illness, emergency injection kit); Medic-Alert identification; and never stopping steroids abruptly.