How does a person know if they are awake or dreaming?

Generally the best way to know whether or not a person is awake or asleep is how they see themselves acting in a dream. While dreaming a person normally is not exactly like themselves, more of an exaggerated version of some of their characteristics. The biggest problem however is while in a dream, unless the person is in a lucid dream, there is not a way of knowing they are in the dream until they wake up.