What do the first two lines in Act 5 of Romeo and Juliet mean?

The first two lines of Act 5 of Romeo and Juliet, spoken by the chorus, are:

If I may trust the flattering truth of sleep,

My dreams presage some joyful news at hand.

These lines foreshadow the events of the act, in which Romeo and Juliet finally reunite and are able to be together. The chorus is suggesting that the events of the act will be positive and bring joy to the characters.