Not all cases of depression include manic phases and there is a clear distinction between depression and bipolar depression:
http://www.ulifeline.org/articles/399-bipolar-depression-vs-unipolar-depression
Mine is unipolar so I speak from a slightly different point of veiw and my comment may well just be my subjective experience.
Personally I do very well to hide my depression (often for months at a time) but I have had a lot of practice.
As for my understanding of the condition, it is something I have lived and dealt with for the past 20+ years so I know a little something abou