NOS=Not Otherwise Specified. It was my dx when I first learned I was BP. It just means that your version of bipolar doesn't fit neatly into any of the other categories (BP 1, BP 2, cyclothymia) and it's going to take time to figure out exactly what kind you have. The diagnosis doesn't mean it's not severe, only that your symptoms don't meet the strict criteria outlined in the DSM-IV.

And even if you do wind up with a "number", it can change. I'm a tentative BP 2 for now, but my doctor hasn't ruled out BP 1 yet because of the severity of my hypo/manic episodes.

Hope this helps. NOS feels like a wastebasket diagnosis and sometimes isn't taken as seriously as 1 and 2.