Freud saw anything hollow as a sexual representation of the womb of the vagina. May represent yourself, or your psyche. Opening the box would them be extremely important for you. May symbolize the unconscious, the fear of the powers within the unconscious (as in Pandora's box). May represent limitations or feelings of being boxed in. If opening the box fills you will fear, you may be uncovering aspects of yourself that make you feel anxious.