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.
The Artist must know how to vary the planets significations according to the year wherein he writes, having still a regard to the grand Epoch of superior Conjunctions or Comets preceding. - William Lilly (1602.-1681.)