How is Hermia's dream a reflection of realit?

She says about her dream (in 2,2) "Methought a serpent ate my heart away, and you sat smiling at his cruel prey." While she has been sleeping Lysander, under the influence of love-in-idleness, has abandoned her for Helena. Hermia's dream that Lysander does not care about her (since he could watch a serpent eat her heart and smile) is a relection of reality.