At one point in my mid-twenties, I realized that I had never cried from joy. It then became one of my life goals - to love something so much that I cried tears of utter happiness. When it did finally happen, I was amazed at the feeling inside. It was joy for sure and it was also painful. The opposites are always in communion.
When you cry from joy, the joy part is obvious, it's the bursting feeling of your heart and soul; the tears, for me anyway, come from actual pain. For instance, Joy: "I love everything about India - it feels like my soul's home." Tears: "It is not my home; I will have to leave." And the obvious one I can only imagine and intuit from friends who have children, Joy: "I love this being with every molecule - seen and unseen - that I have." Tears: "Any pain this being feels will become my pain. And I will sometimes have no way to assuage that pain."
It boils down to taking a risk, whether calculated (like getting on a plane to a place you KNOW you will love with all of your soul) or uncalculated (like having your first child with no real knowledge of the true and palpable sense of having part of your soul living a life outside of your body). And just like Albert Camus says, your capacity for goodness equals your capacity for darkness. I'm sure I'm not the first to point out that your capacity for joy equals your capacity for sadness. The more you invest your heart, the greater the potential for pain.
And as Lloyd Dobler says, "I don't care! I want to get hurt!"
So get on out there, open your heart to its greatest joy, reach beyond the tips of your fingers, love bigger than your mind prefers, and git 'er done!! Cry some sweet and juicy tears of joy!