Think of 'sanity' as something representing safety and comfort ... like a house.
A house with the usual four walls and roof and so on.
For a person to be in that state (of sanity), and since the house represented sanity, that person can be said to be in sane.
You feel good... only because you were thought to feel good when you were growing up. how come you cry when sad and cry when overwhelmed by happiness?
Some people, when overwhelmed (be it positively or negatively) laugh or cry spontaneously, sometimes, both simultaneously.
nai meh meh