Lethargy, anorexia, panting, hind leg weakness, gastrointestinal problems, vomiting
, and hair thinning, were the symptoms that forced you to take your dog
to the vet initially. These symptoms can be signs of endocrine disorders, specifically Hypoadrenocorticism (Addison's Disease), Hyperadrenocorticism (Cushing's Syndrome), and hypothyroid.
I think that your dog may have had undiagnosed Addison’s disease (Hypoadrenocorticism).