why do tears came rushing when you are hurting so much?

Tears flow from our eyes when we cry because they contain chemicals and hormones produced by our bodies.
When we become upset, our brains and bodies overreact and work overtime by producing chemicals and hormones.
Crying helps eliminate these extra chemicals that we don't need.... 
The chemicals and hormones disappear from our body through the form of tears. As our tears flow, they sooth our sadness or distress by withdrawing these chemical agents.
That is why many people feel calmer or more refreshed after crying--because the tears get rid of these hormones that are produced when we are sad, happy, or distressed.