When something is unbelievably beautiful or joyful, you wonder whether it is a dream. Often, what you perceive as reality is not joyful and so when misery is there, you never wonder if it is a dream. You are sure it is real. This is knowing the real as unreal and unreal as real. In fact, all the miseries are unreal. A wise man knows that happiness is real, as it is one's very nature. Unhappiness is unreal as it is inflicted by memory. When you see everything as a dream, then you abide in your true nature.
Payal asks : "What about a nightmare?"
Sri Sri : A nightmare is a dream mistaken as reality. There is no confusion in a dream at all. Keep wondering whether all this is a dream and you'll wake up to the real.