The most common diagnoses that are abbreviated by A.N. are Anorexia Nervosa, Acanthosis Nigricans (skin disorder), and Acoustic Neuroma.
A.N. is pretty vague but my first guess w/o why you were there,
is ANS 'Autonomic Nervous System'. It simply means automatic-
reflex you can't control. Ex: contraction/constriction/eye-
reflexes/BP. Only post I found recent was the sensitivity to
the lights at school causing hdaches. That can be ANS at work.
Sometimes letters will be the Dr's own code for remembering a
thought.
If you search back through the archives for things I've posted, you can see the symptoms that have been going on. It gets rather lengthy, though.