If you are watching an opera in your dream, this suggests that you need to observe the drama taking part around you in waking life.
If you are taking part in an opera, but not singing, this suggests that you need to inject more drama into your waking life.
If you are singing in the opera, you are beginning to express your emotions more fully in everyday situations.
If you hear singing in your dream, this suggests that you are, or need to be, in touch with your emotions and creativity. Singing is a way of raising your vibration to a higher level, emotionally and spiritually.
If you are singing, this is a pure expression of joy and love of life.
If you are singing alone, you have learned to enjoy your own company.
If you are singing in a choir, you are able to express yourself well in a group.
[1]