ELI5 Crying - why do we cry with both sadness and joy?

Why is crying so much more than just being sad? Why do your lungs perform those jerky gasps once the actual sobbing stops? Why does that painful "lump" form in our throats when the glottis tries to stay open for oxygen while we're trying to swallow? How do emotional tears differ chemically from the ones we use for onions, and do they actually "flush" stress hormones out of the body?

... we explain like I'm five

Thank you to the r/explainlikeimfive community and in particular the following users whose questions and comments formed the basis of this discussion: previous-change-4346, josvan135, gynoceros, nimo01, manatee3232, mike2220, tstack123 and lohborn

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