It is obvious from the title that dreams are one of the key themes of the novel. Dreams are central to the chaotic action that occurs in the forest and of course Puck further confuses the boundary between dreams and reality at the end by telling us that if the action of the play has offended us we can pretend that it was all a dream.
However, the end of Act IV represents the end of the dreaming sequence, as all of those affected by Oberon and Puck's magic are restored to their rightfully intended states. The resolution of Oberon and Titania therefore implies a return to rightness and the restoration of a sense of order governing relationships - most profoundly seen in the ceremony of marriage, which joins the various lovers and of course which Oberon and Titania bless.
However, there does seem to be a slightly darker side to these "dreams" - we can see that especially in the case of the 4 lovers, what happens to them in the forest exposes them for who they really are. We see Lysander, who has been up until then defiant about the constancy of his love, become incredibly inconstant. Demetrius is forced to play the role of pursuer of Helena for a change, and the friendship of Helena and Hermia disolves into a catfight. Whilst the end of Act IV therefore signals a return to normality, are left questioning this "happy ending", as Shakespeare has shown us what shallow and inconstant creatures we are.