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What does You turn my whole world upside down mean? Does it mean You disappoint me?
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No, it means that you disrupt or overturn everything that I know and am familiar with.
Comments  
Students: Are you brave enough to let our tutors analyse your pronunciation?
It could mean many things, but they all involve great change. For instance, it could mean:

You have suddenly changed my entire life.
You make me think about everything differently.
You completely infatuate me.
You upset the familiar order of my life.
You destroy the things that are most important to me.
It's often meant with positive associations, like the thrill of falling in love—but can sometimes be negative, describing unwanted change.

Disappointment is not really the same thing at all.
It means that you are head over heels in love and see everything clearly now the rain is gone. You take over a person's life.