Why am i hearing voices in my mind before sleep?

It may be: Hypnagogic hallucinations as you are falling asleep or it may simply be your thoughts.

Since the voice is inside your head it may be that you have an active imagination and this is your way of trying to deal with issues. First have a physical examination by a Doctor to know if you have an illness. Please see a Clinical Psychologist with expertise in multiple types of psychotherapy and a Psychiatrist for medication.