Who Knows Which is Which???

No one can accurately explain how and why dream comes.
When we shut eyes up, we see nothing but dark,
when we begin to sleep, we don`t know what we see,
and when we dream, it seems SO real.

Getting up and consciously knowing we`ve just dreamt something made us happy,
different from who we actually are when open eyes up,
makes an unbelievable question, it`s odd!

Sometimes we remorse why should we wake…
but how could we know which is which?
I mean... how could we know that we are not dreaming right now?
Can you differentiate which is real and which is dream?