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.
Give not judgment before thou knowest the intention of the querent; for many ask they know not what, nor can they express what they intend. - William Lilly (1602.-1681.)