What connotation does Edgar Allan Poe use in his poem a dream within a dream?

"A Dream Within A Dream" portrays the hopelessness that one feels by the passage of time. The speaker tries to hold on to the sand, but it slips through his fingers. The sand symbolizes the time he can not keep. He wants the moment to last forever but it can not. With a parting kiss, the speaker remembers the hope and happiness he once felt and questions whether that happiness was a reality or part of a dream.