Adrenal Insufficiency (Primary or Secondary): This condition is characterized by the inadequate production of cortisol, leading to symptoms such as tiredness, weight loss, and low blood pressure. The isolated low cortisol level is a key indicator of this diagnosis.

Pituitary Dysfunction: The pituitary gland regulates the adrenal glands' production of cortisol. Dysfunction in the pituitary gland can lead to decreased cortisol production, resulting in symptoms like tiredness and low cortisol levels.
Chronic Stress: Chronic stress can lead to adrenal fatigue, a condition where the adrenal glands are exhausted from prolonged stimulation, resulting in decreased cortisol production and symptoms of tiredness.
Medication Side Effects: Certain medications, such as steroids and some antidepressants, can affect cortisol levels, leading to isolated low cortisol levels and symptoms like tiredness.

Addison's Disease: A rare endocrine disorder in which the adrenal glands do not produce enough cortisol and aldosterone. It can be life-threatening if not treated promptly, making it a crucial diagnosis not to miss.
Pituitary Tumor: A tumor in the pituitary gland can lead to decreased cortisol production and other hormonal imbalances. Early detection is critical to prevent serious complications.
Hypopituitarism: A condition where the pituitary gland does not produce one or more of its hormones, including adrenocorticotropic hormone (ACTH), which regulates cortisol production.

Congenital Adrenal Hyperplasia: A group of inherited disorders that affect the adrenal glands, leading to impaired cortisol production.
Familial Glucocorticoid Deficiency: A rare genetic disorder characterized by impaired cortisol production due to mutations in the ACTH receptor gene.
Allgrove Syndrome: A rare genetic disorder that affects the adrenal glands, leading to impaired cortisol production, among other symptoms.