Adrenal hypofuction disorders:
Primary adrenal insufficiency:
It is defined as hypocortisolism due to disorders involving the adrenal glands.

Addison’s disease: 
Addison's disease is an endocrine or hormonal disorder that occurs in all age groups and afflicts men and women equally. Addison's disease occurs when the adrenal glands do not produce enough of the hormone cortisol and, in some cases, the hormone aldosterone. The disease is also called adrenal insufficiency, or hypocortisolism.
It is due to the autoimmune destruction of the adrenal and is the most common cause of chronic insufficiency.
There are deficiencies of glucocorticoids, mineralocorticoids and 17-ketosteroids.
Symptoms: 
chronic, worsening fatigue 
muscle weakness 
loss of appetite 
weight loss
hypotension due to salt loss in the urine
skin changes in Addison's disease, with areas of hyperpigmentation, or dark tanning, this darkening of the skin is most visible on scars; skin folds; pressure points such as the elbows, knees, knuckles, and toes; lips; and mucous membranes
Addison's disease can cause irritability and depression
Hypoglycemia, or low blood glucose, is more severe in children than in adults
In women, menstrual periods may become irregular or stop.
Vitiligo
Abdominal pain

Diagnosis and tests:

Screening test of choice is AM cortisol level. (done around 8AM) 

ACTH stimulation test: 
Most specific test for diagnosing Addison's disease. In this test, blood cortisol, urine cortisol, or both are measured before and after a synthetic form of ACTH is given by injection. Measurement of cortisol in blood is repeated 30 to 60 minutes after an intravenous ACTH injection.
The normal response is a rise in blood and urine cortisol levels. Patients with adrenal insufficiency respond poorly or do not respond at all.

There is an elevated Plasma ACTH.
Hyponatremia and hyperkalemia
Eosinophilia
Fasting hypoglycemia due to loss of lack of gluconeogenic activity of cortisol.

Treatment
Cortisol is replaced orally with hydrocortisone tablets
If aldosterone is deficient it is replaced with oral doses of a mineralocorticoid called fludrocortisone acetate.
Addisonian crisis or acute adrenal insufficiency:

If diagnostic work has not been completed and you have to give steroid supplementation, USE DEXAMETHASONE as it does not interfere with the cortisol assays.

If you have untreated Addison's disease, an addisonian crisis may be provoked by physical stress, such as an injury, infection or illness.
Symptoms of an addisonian crisis include

sudden penetrating pain in the lower back, abdomen, or legs 
severe vomiting and diarrhea 
dehydration 
low blood pressure 
loss of consciousness 
Treatment:
An addisonian crisis is a life-threatening situation that results in low blood pressure, low blood levels of sugar and high blood levels of potassium.
Treatment typically includes intravenous injections of:
Hydrocortisone 
Saltwater solution 
Sugar (dextrose) 

Other causes of hypocortisolism:
Tuberculosis- which can destroy the adrenal glands, accounts for about 20 percent of cases of primary adrenal insufficiency in developed countries.
Chronic infection, mainly fungal infections
Cancer cells spreading from other parts of the body to the adrenal glands
Amyloidosis
Surgical removal of the adrenal glands
Secondary Adrenal Insufficiency
It is much more common than primary adrenal insufficiency and can be traced to a lack of ACTH. Causes: 
A temporary form of secondary adrenal insufficiency may occur when a person who has been receiving a glucocorticoid hormone such as prednisone for a long time abruptly stops or interrupts taking the medication.
Surgical removal of benign, or noncancerous, ACTH-producing tumors of the pituitary gland (Cushing's disease). In this case, the source of ACTH is suddenly removed, and replacement hormone must be taken until normal ACTH and cortisol production resumes.