Crying in a dream often signals release rather than distress -- emotion that's finally finding an outlet after being held in during waking hours. Waking up from it feeling lighter can suggest the dream did some of that processing for you, even if you can't immediately name what the tears were about.
Mars of a nativity, and not joined to good planets, signifieth the native to suffer by envy and hatred. - William Lilly (1602.-1681.)