Singing in a dream often points to authenticity -- your own voice, literally and figuratively, being given room to come through. Singing confidently in front of others can reflect a readiness to be heard, while losing your voice mid-song often names a fear that what you have to say won't land the way you want.
Entrust the Sun when you are depressed because it means renovation, growth, and quick response. - Picatrix (Andalusia, ~1000.AD)