Could somebody be depressed, but not be aware of it?

Depression: Clinical depression has many different symptoms, though one many people think about is being sad or disinterested. Depression can present as a cognitive problem, or change in memory or thinking and many other symptoms, so yes, it is it possible to have aspects of a depressive disorder and be unaware of the problem. See a practitioner to address.

Yes: Depression can present in many ways. For instance, in children - there may be acting out behaviors and anger. Depression may express itself in physical symptoms. Depressive symptoms may not be obvious to the person who is self-medicating with drugs or alcohol. Some people are not particularly in-tune with their feelings.