Depressed? MOI???

Finally got to see El Doctero ... 19 days after being stricken by the Lurgi. He confirmed I had in fact got/had Shingles and gave a lecturette on the whats, wheres and hows of H Zoster Esq.
Apparently this stuff is not used much nowadays, but was intended as an anti-depressant, but one of its more useful side-effects was, apparently, a reduction in the intensity of some nerve messages, thus reducing the effect of said Lurgi.
Or summat of that ilk.

Well, you're bound to look these things up aren't you?
An NHS webpage started by saying
"Before Continuing...
Please select which condition or illness the medicine is used for:
Depression
Mood Disorders
Nocturnal enuresis"
Question ...
WHERE do I go if the answer's "None of the above."?
Damnear every early reference I found aimed it at depression.
:¬((
I wasn't, till I started reading about it.
:¬))

One site did admit
"The exact cause of depression is not known. Anyone can develop depression. It can develop for no apparent reason or it may be triggered by a life event such as a relationship problem, bereavement, or illness. Amitriptyline is not prescribed very often for depression any more, as other antidepressant medicines are usually preferred."