You can either be absent in the bygone or the coming time.
The past or the future sucks life out of the present.
Memories, plans or projects are transformed into reality, while reality becomes emptiness.
The thought makes ifself independent in relation with your reality, and it becomes the whole of reality.
The unreality in this consists in, that you then only really exists in the hope about a richer future, or in the dream about a lost past.