Darkness in a dream usually points to the unknown -- the unconscious part of a situation, or of yourself, that hasn't been illuminated yet. Moving through it without panic can reflect a growing willingness to face uncertainty, while fear of the dark often names a more specific worry about what you might discover if you looked closer.
The Fixed Stars are the most efficacious of all in their operations, for what actions they manifest or occasion are very great. - William Lilly (1602.-1681.)