Cortisol is the missing hormone. It is missing because there is not enough ACTH being made. The lack of cortisol causes you to lose more fluid in the urine, thereby reducing the amount of water in the body. As a result you feel weight loss

You have a problem with the hormone cortisol.
http://endocrine.niddk.nih.gov/pubs/addi...
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.

The most common cause of Addison's disease (also known as chronic adrenal insufficiency, or hypocortisolism) is a rare endocrine disorder. It is the destruction and/or shrinking (atrophy) of the adrenal cortex. In about 70% of all cases, this atrophy is believed to occur due to an autoimmune disorder. In an autoimmune disorder, the immune system of the body, responsible for identifying foreign invaders such as viruses or bacteria and killing them, accidentally begins to identify the cells of the adrenal cortex as foreign, and destroy them. In about 20% of all cases, destruction of the adrenal cortex is caused by tuberculosis. The remaining cases of Addison's disease may be caused by fungal infections, such as histoplasmosis, coccidiomycosis, and cryptococcosis, which affect the adrenal gland by producing destructive, tumor-like masses called granulomas a disease called amyloidosis, in which a starchy substance called amyloid is deposited in abnormal places throughout the body, interfering with the function of whatever structure it is present within or invasion of the adrenal glands by cancer. Symptoms of Addison's disease include severe fatigue and weakness, loss of weight as a result of the lack of sufficient cortisol, increased pigmentation of the skin. Blood tests can lead to the diagnosis of Addison's disease. Patients are given a testing dose of another hormone called corticotropin (ACTH). - Treatment for Addison's disease involves replacing the missing cortisol and providing replacement therapy for the missing aldosterone.( a hormone secreted by the adrenal cortex which affects blood pressure and saline balance. The hormone renin, which is produced by the kidney, helps to regulate the release of aldosterone, and renin levels are often compared with aldosterone levels for diagnostic purposes) The disease demands treatment, for without it death will result.
Hope this helps
Matador 89

Addison's disease (also known as chronic adrenal insufficiency, or hypocortisolism) is a rare endocrine disorder which results in the body not producing sufficient amounts of certain adrenal hormones