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.
There will be some impediment about that part of the body represented by that sign which was afflicted at birth. - William Lilly (1602.-1681.)