The Heiligenstaedter Testament, which I have been
reading and re-reading impresses me as a reflection
in a very awkward and imperfect literary style of that
same tumultuous emotional experience which Beethoven
was able to express in music with such magical effect.

In the Heiligenstaedter Testament, Beethoven blames his
hearing loss for his social isolation. I find it noteworthy
that Beethoven makes an issue of keeping his hearing loss
a secret in society. The circumstance that in 1802, Beethoven
was (still) able to conceal his deafness, suggests that
in that year, the hearing loss cannot have been very severe.
At what rate, and in what stages the deafness progressed
in the ensuing 22 years and how it was affected by
Beethoven's other illnesses, seems to me very uncertain. 

Whatever the organic, somatic basis of his hearing loss,
the emotional component seems, at least sometimes, to
overshadow physical illness. The suffering which Beethoven
recounts:

"wahrhaft elend, einen so reizbaren Koerper,
dass eine etwas schnelle Veraendrung
mich aus dem Besten Zustande
in den schlechtesten versezen kann"

(truly miserable, so irritable a constitution,
that any somewhat precipitous change
can transport me from the happiest condition
into the most wretched state)

is the description of mental turmoil to which
progressive hearing loss might contribute
but which deafness alone cannot explain.
It's not an argument which I choose to make,
but it must be recognized as plausible, that
given Beethoven's mercurial passions, much,
if not all of his "deafness" might have
an emotional rather than a physical basis,
might, in other words, in contemporary medical
jargon, be functional, or in antiquated words,
"hysterical". I can't tell. The relationship
between Beethoven's hearing (loss) and his
music seems to me a holy mystery.