Help please! is excessive writing a sign of schizophrenia or bipolar?

Could be. Others?: If this is the only unusual thing, probably it is not a serious mental illness - which those are. If there are other troubling things too, they could be signs that help could be needed. Is the writing itself disturbing, troubled, repetitive? Or, is it creative or useful? These make a difference. Ask someone to help you evaluate this so that you can find help if it is a serious condition.

Maybe, maybe not: I agree with dr. Weixel that there are many possible causes for excessive writing. Also "excessive" may be in the eye of the beholder. Witness authors trying to complete a novel, for instance! to understand what's happening, one needs to review the writing itself and place in context with all else about the person. Some people with complex partial seizures also manifest excessive writing.