How do you know that your dreams is not the reality?

there is no definite way to tell that your dream is not reality
or that when you think you are awake that you really arent asleep

Sometimes people confuse old memories with dreams they had.

It be even impossible to tell if reality you live in is real reality and not something your brain created.
People that are insane create their own realities and they arent aware of it.
How could you be aware that you yourself arent insane
it would not be possible if you were