Hi Aliya, that b12 level number of 400 something is on the low side. It may not be flagged on the blood test results because the US has a lower acceptable number than other countries. here is a website of a person who has posted on boards for years and whos research in b12 has helped many posters here and on other boards
http://roseannster.googlepages.com/

b12 is needed in order for damaged nerves to heal and its deficiency can cause many symptoms. I have no idea if it is contributing to your problems but it is something to check out and is easily treatable.
Also since you have dryness of the eyes have you checked out or been tested for sjorgens?

As far as your being afraid of the unknown that is perfectly understandable and something all of us have experienced. Try not to drive yourself crazy while researching on the internet. There is a lot of inaccurate and conflicting information out there. It helps in order to get ideas on what is possibly going on but try to stay calm since fear and stress only make PN worse.