What is bipolar nos and is as serious as bipolar disorder?

Yes: I believe that "nos" appended to any diagnosis stands for "non-specified", and is a coding and billing term used to indicte that the doctor has chosen not to subcategorize the disorder, in this case a bi-polar disorder. As such, "nos" provides no insight about seriousness.

Bipolar Disorder NOS: Although the diagnosis of bipolar disorder not otherwise specified is often less severe then bipolar i or ii disorder (because the person didn't meet dsm criteria for either) that isn't always the case. It could occur because the person was previously diagnosed with a psychotic disorder or possibly because there is concern that substance abuse or a medical condition was causative.