Three levels in Advaita Vedanta

They are ‘Pratibhasika’, ‘Vyavaharika’ and ‘Paramarthika’.

Of these Pratibhasika is the most unreal.

Dream is in Pratibhasika level. In dream we perceive different things.

But in a strict sense, dream is not completely unreal because for things, which we sees, in dream, have - (external substratum in the phenomenal world}.