At the start of act 5, scene 3, the reader should get the impression that Juliet is pretending to be dead. That's because she is following Friar Laurence’s plan. Juliet will consume a sleeping potion and people will think she’s dead, which will allow her and Romeo to secretly escape.
Even when she’s pretending to be dead, the reader gets the impression that neither Paris’s love nor Romeo’s love for her has decreased. Her fabricated death has turned Romeo into a “desperate man.” Meanwhile, Paris aims to avenge his “love’s” death by fighting Romeo. Paris has the impression that Juliet’s grief over the death of Tybalt (killed by Romeo) led the “fair creature” to her death.
Of course, Paris’s impressions and Romeo’s impressions are erroneous. If they had known that Juliet wasn’t really dead, perhaps Paris wouldn’t have tried to fight Romeo, Romeo wouldn’t have killed Paris, and then Romeo wouldn’t have imbibed the actual poison.
Once Romeo kills himself, Juliet wakes up. The reader gets the impression that she is confused and excited.
O comfortable friar! where is my lord?
I do remember well where I should be,
And there I am. Where is my Romeo?
Her use of the possessive “my” impresses upon the reader the extent of her love. She loves Romeo so much that it’s as if he belongs to her. She owns him: he’s hers. The final question in the quote alerts the reader that she doesn’t know what has happened to him. She isn’t aware that her Romeo is dead.
When she discovers he’s dead, the reader should get the impression that Juliet is determined to kill herself (for real, this time) as well. When Juliet picks up Romeo’s knife, she exclaims, “O happy dagger!” This declaration reinforces the impression that Juliet’s happiness is inseparable from Romeo’s: since he’s dead, she must die, too.