A coffin in a dream rarely predicts death literally -- it more often marks an ending you're processing, or feelings you've buried rather than let yourself fully grieve. An open coffin can point to something from the past resurfacing, while a sealed one often reflects a chapter you've genuinely closed.
Consider what things the Planets perform not by their Aspects, and observe if they do them not by their Antisions, for the Antisions have power, and are not to be enumerated amongst Aspects. - William Lilly (1602.-1681.)